Night Market | Action - Duration | $4
The next time you buy a Curse, trash this.
While this is in play, you can't buy Provinces, and at the start of your turns +$1 +1 Buy
It's kind of like a treasury, sitting around and giving you $ and a buy every turn! Well, maybe it's kind of like a Market. Except, you can't buy Provinces when it's in play, you'll have to buy a curse to trash them -- they are immediately removed from play so that means the turn you buy a curse you can buy Provinces. Good thing they have a +Buy. You could also attempt to forgo Provinces entirely, trying for a 3-pile with alt victory cards.
Costing them at a $4 with the knowledge that once you start greening they go away, and comes with the expense of a curse in your deck.
I'm open to feedback. Treasury is quite weak for a $5 -- is this un-fun strong for a $4? I'd consider making it gain a Copper when you trash it but that might be
too prohibitive. I think the cost may work as is, since it is terminal and does nothing on your first play.