I'm not sure you got the right higher levels upgrades for this spell, but otherwise seems like a fun idea to spend money to attack with.

I love the idea! I really love it, but it seems overwhelmingly under-powered, even for a cantrip.
Don't get me wrong however; even as is, I'd love to give this cantrip to a street urchin rogue child just for the meta hilarity of it.

With the exception of Vicious Mockery which does 1d4 psychic damage (but grants disadvantage on the target's next attack roll), all other damaging cantrips do at least 1d6 base damage, without a consumed material component (especially one with a value literally expressed in coins 🤣). Quite a few start at 1d8 and a few start at 1d10. Spending so much in consumed material components every to you attempt to deal that much damage is a huge financial handicap that can be easily avoided by learning any other damage cantrip. All damage cantrips have some special effect or feature to them that give them flavor and utility beyond number crunching at a target. This write up shares edlritch blast's ability to target separate individuals, which is great. It's nice to have a cantrip available to non-warlocks that does that, but even though bard's and wizards can't use eldritch blast normally, I don't think this cantrip competes well with others available to them. Maybe consider how the cantrip would look if the damage scaled differently. Throwing away copper coins is fair. Unless a party is completely destitute and unwilling to illegal their way to better times, copper coins will never matter. That said, extremely low base damage at the cost of cash, even for the trade off of dealing force damage... I don't think can compete with any other cantrip.

I suggest scaling up from 1d4 base damage with no modifiers, and adding a +1 modifier to hit or damage per value upgrade of the coin. Making the cantrip more likely to hit or more forceful when it hits, gives the player a choice. It makes it a more versatile cantrip, and gives the player a reason to invest in it. Sometimes they need need need to hit, and sometimes they need need need the damage. It wouldn't overpower the spell in any way when you compare it to other spells (especially considering the cost), but does make it more enticing to players who like to plan for different situations.
You could throw a copper coin for 1d4 force damage, a silver coin for 1d4 damage at +1 to hit or +1 to damage, a gold coin for +2, or a platinum coin for +3.

I don't anyone uses electrum, but fiddle around with the stats a little. My point is, the unique thing about this cantrip is that it's weak and cost money. That's interesting narratively, but mechanically, its a bad investment. It can target more people at higher levels when it gets more powerful, but the cost of using it scales up too.

Cantrips also all get more powerful at 5th, 11th, and 17th level, rather than at 8th and 16th. Breaking the mold in that way just makes the spell less viable.

this cantrip is cool, but doing 1d12 of force damage for 10gp is unreasonable, an eldritch blast does basically that for free.  If I were to edit it, I would start with a copper doing a d6 at least (cause it destroys the coins) then upping a silver to do a 1d12, Electrum 3d6, gold 2d12 and platinum, 4d12.  (perhaps 4d12 is to high, but it needs to be more worth the cost of the coin)  Either that or leave it as it is and make it so it doesn't destroy the coin, that way you can get it back, but any coins used you have to have a investigation check of 15 or something to find.

know what I am going to leave that as my over powered idea here is another alternative

Copper 1d4+1 force damage, Silver 1d6+3 force damage, Electrum 1d8+5 force damage, Gold 1d10+8 force damage Platinum 1d12+12 force damage  that way the coins value can add definitive damage to it.

I really like the idea of this spell, using coins to deal damage, but like the others said, this gets really expensive, really fast.

I created a USD > gp conversion rate to give me an idea of how much things should cost on the fly. (It works... look at the price of "lodging" in your area and compare)

1 cp  = $0.50
1 sp = $5
1 gp = $50
1 pp = $500

So, yea, if I'm going to spend $5 casting a cantrip to deal damage, it better be dealing something worth it, at least Eldritch Blast damage.

Constructive Suggestion:
Rework the damage table somehow so that we're dealing more damage for spending hard-earned cash on at-will cantrips.
At Higher Levels: Increasing damage per coin is probably more appropriate than spending more per casting.

I'd love to see what you think of a new spell I designed recently, please comment: Illusive Wounds

I agree it is a bit under-powered. I like Jety_Lefr's idea of scaling from a d4 to d12, including potentially a +1 modifier to all (so silver would be 1d6+1 damage). That would make it on par with most damage cantrips, depending on the material investment. For Gold and Platinum, it would be quite expensive but also very effective for a cantrip. Also agree about the level scaling, that should be kept in line with how it normally is.

But the idea is unique and good, so still gonna upvote :)

Quote from speedy01247 >>

this cantrip is cool, but doing 1d12 of force damage for 10gp is unreasonable, an eldritch blast does basically that for free.  If I were to edit it, I would start with a copper doing a d6 at least (cause it destroys the coins) then upping a silver to do a 1d12, Electrum 3d6, gold 2d12 and platinum, 4d12.  (perhaps 4d12 is to high, but it needs to be more worth the cost of the coin)  Either that or leave it as it is and make it so it doesn't destroy the coin, that way you can get it back, but any coins used you have to have a investigation check of 15 or something to find.

know what I am going to leave that as my over powered idea here is another alternative

Copper 1d4+1 force damage, Silver 1d6+3 force damage, Electrum 1d8+5 force damage, Gold 1d10+8 force damage Platinum 1d12+12 force damage  that way the coins value can add definitive damage to it.

 I'd do, 1cp = 2 force damage, 1sp = 1d6 force damage, (screw electrum), 1gp = 1d10 + 2, 1pp = 2d8 + 4.
Also it'd "level up" the same as Eldritch Blast and other cantrips.... And the cost isn't per shot... That's stupid to pay 3pp/30gp/300sp/3000cp for 3 chances at hitting something...
Since I could just take a feat or multi-class 1 time into Warlock... On average you'd use this spell 2-3 times a non-deadly/boss combat. That's at least 3 gold at levels 1-7...
You start with at best like, 20gp at level 1, if the DM allows it, maaaybe like 100-150gp. Which is less likely than getting a ring of protection (+1) at the start.

Or It could cost 1 gold in general and be just like Eldritch blast, but only cost 1 gold for the entire casting. If you want to have that "cost" go up.
5sp = 1 shot, 1gp = 2 shots, 15sp = 3 shots, and 2gp = 4 shots.

[Revivify is 300gp. Compare the usefulness. A reviving spell, or 30 shots of 1d12 with the chance of at least half missing.]

Ultrakill

Ah, the steel misting spell. It's a shame it doesn't require you to eat ground up steel. 

Me when V1: