now, reading the title you might think this is self evident, it says in the PHB that buying an brand-new empty spellbook is 50gp, but hang with me. You start the game as an wizard with 50 gold pieces, as well as six spells, but here is the tricky part: how do i calculate the value of the spells already in my spellbook? copying an spell into an spellbook takes an certain amount of gold depending on the level of the spell, your wizard subclass and other factors, but tends to be at 50 gold pieces per spell. Your six spells cost you nothing, but it is at least implied that your wizard character has in the past made some kind of investment to get those six spells in his or her spell book, unless they stole the spellbook from somebody else. The six starting spells presumably tell the story of your wizards prior research.

This now leaves the question: for the purposes of the artisans blessing feature (see the forge domain feature for more details, but you are able to copy or create an nonmagical object worth no more than 100 gp, and the ritual can replicate an nonmagical item that contains metal), does all spells added to your spellbook count towards the spellbooks total value, or only spells you copied into the spellbook from another written source? Becuase if spells you added to your spellbook for free do not count towards the value of an spellbook, an forge cleric can copy the entire wizards spellbook for the low price of 50 gold pieces and over the course of an hour, provided that your spellbook contains at least an little bit of metal, like having an little lock and key on it to hold it shut like you see in some diaries. This means that if your dm rules in the favor that only copied spells add value to an spellbook (an reasoning that is partial nonsense) then you can potentially make as many backup spellbooks as you want and just store them everywhere and anywhere.

of course, with "value" you can defenetly argue that if an spellbook ever was for sale, the more spells it contains and the more rare/ powerful those spells are, the more attractive the spell book would be for consumers and therefore it would have an higher demand and thus an higher price

the cost of adding a new spell into your spell book is partially the result of the rare, expensive inks needed to document an spell, but this can not fully explain the cost of copying an spell into your spellbook for three reasons: one, the cost of copying a spell decreases depending on subclass and school, how the **** are you conserving so much ink with transmutation spell? second the ritual caster feat mentions how part of the cost of copying an spell is the cost of experimenting with the material components needed to cast it. While the feat is not the same as the way wizards casts spells, an ritual book is indeed much like an wizards spell book and is treated in much the same way. And thirdly spells you scribe into your book with your own research  (that is to say, the wizard spells you gain from leveling up) cost such an small amount in the ink needed to scribe it down the players handbook does not even bother with it. (that and forcing you to pay money for an feature other classes get for free is an dick move, so maybe it has more to do with balance than lore)

I would rate the cost of a spellbook to be at least the cost of creating it, meaning a spellbook with even a single spell in it would be worth a minimum of 100gp.  Wizards can get around that cost by adding spells through leveling, but I wouldn't include that in the value of the object.

Edit: I haven't played a 5e wizard yet, so didn't notice the bit on copying a spellbook at 10gp per spell level.  I might consider allowing the copying, but the price tag is going to be such that it's unlikely to be worthwhile.

so, you are saying that an wizard that was just starting out whould have to copy the first few spells he knows from another source, thusly those first few spells would cost him an hefty amount, but that after that new spells gained via the wizards own advancements and invetions into magical research should not add value to the spellbook? thats one way to think of it but at the same time that seems like thats an inconsistent way to look at it, since your six starting spells are also "free", mechanically at least

of course, the channel divinity option mentions that it seeks "the value of the creation" or whatever, so the cost of making it, and to that end you might judge it based on how expensive it would be to simply write down each of the spells using rare inks into another book, or 10gp per spell, and use that as the value of an spellbook for the purposes of artisans blessing since 10 gp per spell level is probably the best representation of the raw cost of simply writing stuff into your book, since it is the cost that seemingly ignores all "research fees" that seem to be included in the cost of copying an spell into your spellbook from another wizard, the whole "there is no standard system for writing down spells, so i need to spend a bunch of time and money to decipher the components in these spells from what they have written, then spend a whole lot of time to experiment/ research/ troubleshoot the spell"

furthermore, when you say "allowing the copying" do you mean allowing an wizard to copy his spells at all? an feature that is supremely important to an wizard in case their book is destoryed? or do you mean copying an entire spellbook with channel divinity: artisans blessing?

also this leaves the question: if a lot of the cost comes from trying to figure out how this other wizard "sees magic" and how they choose to write down spells, would it be easier to copy an spell from an fellow wizard if we both use the same system, if we both come from an very strict wizard school where we write down our spells in the exact same way, and use an verry scholarly and standardized language? would it be easier to copy an spell if you have prior experience with this particular wizards spell notation system, if you are an archaeologist /historians wizard who has been studying the same long dead author for an long time, learning about his life and how it shaped his views on magic and learning that wizards system better than your own? would it be easier for you to decipher and understand another wizards writings if you have the linguist feat? should we not have an more complicated system for this than a mere 50 gp for other wizards, 10 gp for your own, and the time is halved if the particular spell is of an school of magic you have experience with? should we not have an better, more unique system that really delves into how easy or hard that could be?

I'm saying the ones from leveling up would add value to the spellbook even though they don't cost the wizard to add them.  As for the "allowing the copying" I didn't notice the reduced cost for copying from your own spellbook instead of another source, if it were 50gp per spell level, any spell would put it over 100gp.

Few things...

1) Artisans blessing reads like you can only make metal objects so if you made a spell book it would have to be metal cover, metal bindings and metal pages. Although you could make one I would say it would appear as a brand new blank spell book and it would not copy any spells in it. There was a similar query on a sage advice a while ago about whether you could create diamond rings using the ability and build up a stock pile for things like revivify and raise dead, the result was a no, its not in the spirit of the ability, and that the list of "a simple or martial weapon, a suit of armor, ten pieces of ammunition, a set of tools, or another metal Object" are the things you can make not a list of examples, so you could make a grappling hook but not he 50ft of rope with a grappling hook attached to it.

2) The notion of "value" is a bit of a strange one as you can throw lots of money at creating something but that is no guarantee of a quality product or that others will find it valuable and be willing to pay for it. So assigning a value to a wizards spell book is hard. It is worth a fortune to the wizard that spent time and resources filling it with spells but to you average pick pocket it will likely be something that they can sell and get enough money for a couple of hot meals and little else. The value of the spell book you start with is a little redundant, there are ways of getting it that are down to back story, Wizard implies you have some sort of training, whether that be master/apprentice, previous role as sage/librarian to an arch mage, harry potter wizard school graduation present etc. The 6 spells and cantrips you start will cost the character some money/resources in their background in the same way a fighter spent time learning to fight with different weapons and use various types of armour and a paladin spent time learning a doctrine and going through their trials to be come a paladin.

3) The cost of adding spells to a book become cheaper when scribing spells of your chosen school because you are specialized with them. I view scribing a scroll to be the act of creating a a sigil/glyph that encodes the magical formula on to the page. The discount comes form the wizard specialty, a transmutation wizard scribes a transmutation spell and can see subtle ways to improve the glyph they make where a Evocation wizard scribing the same transmutation spell has to dogmatically follow what the scroll says and vice versa.

4) as for having a more complicated system for spell creation..make it as complicated as you want for your game, I played in a live action role-playing system for many years where divine magic had one alphabet (based on Norse runes) and arcane (not sure what it was based on but was hard to read) had another and if you couldn't read it in character you didn't know what it said (and you were not allowed to use a crib sheet with translation either).

1) yes i will agree that it is defenetly against the spirit of the rules, and the ability does mention how the ability can forge nonmetal parts of the created item, such as creating an wooden shaft to an metal spear or something similar, and XGE provides several strange forms your spell book can take, such as an completely metal book where spells are etched in with acid, and also an spellbook thats just a bag full of rocks and you etch your spells onto those rocks.

2) i agree on you completely on point two

3) so standardized terminology and esoterica that you know both other wizards might not? I still feel that the idea of an "research fee" is more accurate, that the cost represents time and money spent experimenting until you have fully understood the spell, since it explains both the cheaper price depending on arcane tradition (you simply understand them better and need fewer tries before you "get" it) and it explains why it is so much cheaper to copy over your own writing (you literally just copy and paste).

4) thanks for the encouragement, that sounds kinda interesting