Oh man, so i should comment on other cards, too?
Bronze Worker
Types: Action
Cost: $4
+2 Actions
Discard any number of copper. +1 Card and +$1 per Copper discarded.
This feels like it would be okay for $2, like Cellar. It keeps you the coins of your Coppers at the beginning (but can't discard the Estates nor really uses the action) while giving you an additional action later (without being actually good at sifting at that point). It would be nice, but costing $2 and caring about Copper is a bit un-Prosperity in my book.
Collector
Types: Action
Cost: $4
+1 Action
You may play a Treasure card from your hand.
Draw until you have 4 cards in hand.
Each other player may discard a card.
I don't really like the interaction, because it's useful only if you also go for the card. The concept of playing a Treasure and drawing after that is nice, though. I have seen it before on a card by Co0kieL0rd, so it's probably not as unexpected. Still neat and Prosperity-ish.
Consortium
Types: Action
Cost: $7
+2 Actions
Choose a number up to 8. Each player may draw until they have that many cards in hand. Choose a number down to 3. Each player who drew discards down to that many cards in hand.
So, you harm yourself that way? Huh, i'm not sure how appropriate the cost is. I wonder whether this is tested. Either way, it's an attack that lacks the attack type, and i really can't say i like that. People always appear to think an attack is less of an attack when it hurts itself, but it only makes it a bad attack. Sorry.
Desert City
Types: Action
Cost: $5
You may discard an Action card. If you do, +3 Cards, +2 Actions; if you don't, discard a card.
You may discard a Treasure card. If you do, +$3; if you don't, -$2.
You may discard a Victory card. If you do, +2 VP; if you don't, discard a card.
This could be soooo much easier if you make the second option discarding too and reformat a bit:
Discard a card. If it is an Action: +3 Cards, +2 Actions
Discard a card. If it is a Treasure: +$3
Discard a card. If it is a Victory: +2VP
Either way, it has too much going on AND gives you VP without doing anything to progress the game. In fact, it allows you to re-draw that same card the same turn and discard it again for VP. It's not even "monument"-ally weak without the VP option. No fun.
Divdends
Types: Treasure
Cost: $7
Worth $1
When you play this, gain a Treasure costing less than it, putting it into your hand.
So incredibly strong... It's almost Platinum AND gains Golds. Sure, you don't always want Gold - but that's partly because Gold has an opportunity cost - something this card practically removes. Very Prosperity-ish, though.
Entourage
Types: Treasure – Victory
Cost: $7
Worth $2
When you play this, choose one: +1 VP; or reveal any number of Victory cards from your hand and +$1 per card revealed.
Worth 1VP
Too much like Plunder in my opinion. Sorry.
Fun fact: "Plunder" in german means "useless stuff".
Exchequer
Types: Action
Cost: $5
Gain a treasure costing up to $6 to your hand. You may put your deck in your discard pile.
Each other player may gain a Silver on their deck.
Not bad. It has friendly interaction and money, so it's very Prosperity-ish. I'm not sure it's that exciting, though - everything on it has always been there.
Grand Canal
Types: Action
Cost: $7
+2 Buys
+$2
All cards cost $2 less this turn, but not less than $0.
You may trash a Treasure other than a Copper from your hand. If you don't, trash this.
This feels a bit wonky. As if it could have worked just fine as a $7-Bridge reducing prices by $2, and someone wanted it too have more going on.
Heirloom
Types: Treasure
Cost: $3
+1 Buy
If this is the first time you've played Heirloom this turn, each time you spend $4 or more with one buy, cards cost $2 less (but not less than $0) for the rest of the turn.
I like the idea, but not a great fan of the execution. For example, i wouldn't limit it to one Heirloom per turn, and talk about the card's cost instead of what you spend. Overpay isn't relevant enough for a wording to go that distance. I can't really think of a way to fix it up, but if there's a simpler wording, i think it's a cute idea.
Investor
Types: Action
Cost: $5
+1 Action
Discard any number of Treasure cards. For each card discarded, +1 Card and +$1.
This suffers from me having seen two "remove coins for draw"-cards before... If i try to be fair, i think it's okay, but probably a bit weak. I mean, it's like a more restrictive Cellar that gives an additional bonus. On the other hand, Vault is an improved Secret Chamber for $5 and had to be nerfed. I guess this is fine if you can repeatedly discard your money for more cash, as it will make your engine capable of running with little treasure cards - what sucks is if you draw this without other Treasures, as this makes it a stop card. I'd be in favour of making this able to discard other cards or costing less.
Metropolis
Types: Action
Cost: $7
+1 Card
+2 Actions
Treasure cards other than Copper produce an extra $1 this turn.
I get why you'd exclude Copper here, as getting 4 Coppers in hand early is really easy - especially if you can use some terminal draw with this. The name is also cute. I'm not sure the parts really interact that well, but i guess what you can do is go for Silver and terminal draw, hope to hit $7 as early as possible, and then buy Provinces. I'd have to try it out, though.
Minister
Types: Action
Cost: $6
All cards cost $1 less this turn, but not less than $0.
You may gain a card costing up to $4. If you do, each other player gets +1 VP.
So this is combines two concepts that are even better in combination and makes up for it with friendly interaction. Also it costs $6, gains expensive stuff and uses VP, (very Prosperity-ish) and cleanly implements the self-Curse concept. I admit it looks a bit "I dunno"-ish, but King's Court doesn't look as strong as it is on first glimpse, either - right? My experience is that it's fun to play and not actually weak.
Other cards later, probably.