I am interested in being a DM but, like most people, I'm on a budget and cannot afford all the books. I'm interested to know what you guys who have DM'd think about which books I need to buy. Obviously the Dungeon Master's Guide is a given, but I'm also thinking about Xanathars Guide To Everything and Volo's guide to monsters. Those three give the most extra content (Class archetypes, races, etc.). However, I want to buy these three digitally since 1) they cost less and 2) I already use DnDBeyond a lot for character creation. I own the Players handbook physically and could borrow the Monster manual from a friend. Although, since I don't own the players handbook digitally, I cannot get all the content from it on this site but really would like to. 

I tend to ramble so I guess my question is: What books should I buy if I want to DM and get as much content as possible?

Question. Do you want to make your own homebrew adventure or run an existing WoTC module? 

The reason I ask is that, I'd argue you wouldn't need a Dungeon Master's Guide if you're running a WoTC module such as Curse of Strahd or Tomb of Annihilation. If you want to make your own custom, homebrew game then the DMG offers some helpful resources, but in my experience, the book isn't absolutely necessary to run the game -- The core rules of the game are entirely in the Player's Handbook, tips for how to run a D&D game are free on YouTube. 

Xanathar's and Volo's are similarly helpful materials, but not necessary for running the game. I ran games for a long time with only a Monster Manual, the Player's Handbook, and whatever module book I was using at the time.

But your answer to that question at the beginning of this post would be helpful information to know before giving much more advice.

I'll second LightSpeed's reply. There was a similar question last month that I'm including my reply to for the general content. Also, consider the library suggestion at the end of that portion. 

Specifically for you, the MM for your monster stats and the DMG will give you a good place to start. DMG does have loot tables and a cleric and paladin subclass. There is some lore, but I reference SCAG and the Player's Handbook more for details. It's nice to have access to the other books, but don't feel like you have to provide all the resources. XGtE does have some nice DM aids and it has many class options and spells. Volo's and Mordenkainen's both have racial options and additional lore/monster blocks.

Here's the other reply:

 You can get the basic rules off of Wizards of the Coast's D&D page, which is a watered down version of the Players Handbook, or the Starter Kit comes with it, a watered down version of the Dungeon Master's Guide, the Lost Mine of Phandelver adventure, and a set of dice. It typically runs for under $20. After that, my suggestion would be to get the Player's Handbook and the Dungeon Master's Guide in some order, followed by the Monster Manual for the stat blocks. The Elemental Evil Player's Companion is also a free download.  After that Sword Coast Adventurers Guide has some great lore along with some players options. Volo's Guide to Monsters and Mordenkainen's Tome of Monsters both have some good lore, additional monster stat blocks, and some player race options. Xanathar's Guide to everything has some class options, additional spells (including all those included in the Elemental Evil),  some content for player backstories, and it revisits some dungeon masters guide topics and gives some great aids. The Guildmasters Guide to Ravnica includes player options and DM guides if you want to use the MTG plane. The rest of the current books (unless I'm forgetting one) are adventure modules. Nothing that I've mentioned after the Monster Manual is needed to be a DM. Having a decent comprehension of the three core books will help the most outside of actual experience. Don't worry if all of your rulings aren't correct, you'll probably forget many rules initially and realize it later. It's not a big deal as long as your players are having fun. Just try to remain consistent with your rulings in a campaign or acknowledge that you made an incorrect ruling if you want to use the proper one going forward.  Also, consider checking your local library to see if they have a copy available. Mine has at least one copy of the core books, though they are all checked out

Thank you for replying, and to specify: I'm wanting to run a home brew campaign.

Quote from LightSpeed >>

Question. Do you want to make your own homebrew adventure or run an existing WoTC module? 

The reason I ask is that, I'd argue you wouldn't need a Dungeon Master's Guide if you're running a WoTC module such as Curse of Strahd or Tomb of Annihilation. If you want to make your own custom, homebrew game then the DMG offers some helpful resources, but in my experience, the book isn't absolutely necessary to run the game -- The core rules of the game are entirely in the Player's Handbook, tips for how to run a D&D game are free on YouTube. 

Xanathar's and Volo's are similarly helpful materials, but not necessary for running the game. I ran games for a long time with only a Monster Manual, the Player's Handbook, and whatever module book I was using at the time.

But your answer to that question at the beginning of this post would be helpful information to know before giving much more advice.

Quote from Jhfffan >>

I'll second LightSpeed's reply. There was a similar question last month that I'm including my reply to for the general content. Also, consider the library suggestion at the end of that portion. 

Specifically for you, the MM for your monster stats and the DMG will give you a good place to start. DMG does have loot tables and a cleric and paladin subclass. There is some lore, but I reference SCAG and the Player's Handbook more for details. It's nice to have access to the other books, but don't feel like you have to provide all the resources. XGtE does have some nice DM aids and it has many class options and spells. Volo's and Mordenkainen's both have racial options and additional lore/monster blocks.

Here's the other reply:

 You can get the basic rules off of Wizards of the Coast's D&D page, which is a watered down version of the Players Handbook, or the Starter Kit comes with it, a watered down version of the Dungeon Master's Guide, the Lost Mine of Phandelver adventure, and a set of dice. It typically runs for under $20. After that, my suggestion would be to get the Player's Handbook and the Dungeon Master's Guide in some order, followed by the Monster Manual for the stat blocks. The Elemental Evil Player's Companion is also a free download.  After that Sword Coast Adventurers Guide has some great lore along with some players options. Volo's Guide to Monsters and Mordenkainen's Tome of Monsters both have some good lore, additional monster stat blocks, and some player race options. Xanathar's Guide to everything has some class options, additional spells (including all those included in the Elemental Evil),  some content for player backstories, and it revisits some dungeon masters guide topics and gives some great aids. The Guildmasters Guide to Ravnica includes player options and DM guides if you want to use the MTG plane. The rest of the current books (unless I'm forgetting one) are adventure modules. Nothing that I've mentioned after the Monster Manual is needed to be a DM. Having a decent comprehension of the three core books will help the most outside of actual experience. Don't worry if all of your rulings aren't correct, you'll probably forget many rules initially and realize it later. It's not a big deal as long as your players are having fun. Just try to remain consistent with your rulings in a campaign or acknowledge that you made an incorrect ruling if you want to use the proper one going forward.  Also, consider checking your local library to see if they have a copy available. Mine has at least one copy of the core books, though they are all checked out

To add to the others. The DMG isn't a given actually. Most rules you need are in the Players Handbook. Then get Monster Manual. And you're good to start.
Xanathar's Guide to Everything is the next you can get. With more detailed rules, loot tables and basically being the DMG, but updated and more useful.
Mordenkainen's Tome of Foes is the last you "need" with more information regarding planes, wars and more cool monsters.
Volo's is nice to get last and round things out with a few more player races, also monsters to use as player races, and some more monsters.

After going through the monster manual, and watching some YouTube videos, I'd say I'm the same as you. I got so many ideas for encounters and quests just by looking at the artwork for certain monsters. All those diverse and interesting monsters gave me so much inspiration! One of the demons I want to use (Maurezhi) is in the Tome of Foes, so I'm going to have to pick up that book. Volo's Guide is probably going to be my second choice because, like you said, of all those monsters and lore goodness. Thank you for replying btw! It's great to get help from experienced DM's!

I have mentioned this before in other forums. I work for a library and we do have some D&D books that can be taken out by patrons. If your local library does not have them, they may be able to do an interlibrary loan to get then. Its worth a shot and can get you reading the material until you can afford to make a purchase.

Quote from Shadowblade25 >>

I have mentioned this before in other forums. I work for a library and we do have some D&D books that can be taken out by patrons. If your local library does not have them, they may be able to do an interlibrary loan to get then. Its worth a shot and can get you reading the material until you can afford to make a purchase.

And the library might have meeting rooms where you can run your sessions...so just borrow the books for each session :)

If you're just starting out, I'd say to start with the basic Core Set. XGtE, Volos, and the others are cool resources, but there's plenty to keep you going for a while in the core books.

Also, check out the DMs guild. It's an awesome site, with a ton of user created materials, and it works well on a budget. There's a lot of material on there for free, pay-what-you-want, and for dirt cheap.

In addition to the good advice above, remember that the books aren’t everything. There is a trove of good advice (and plenty of crap, so be critical) on world building, running encounters, and creating stories and meaningful personalities out there.