This is a kingdom card idea I had the other night, and I would be surprised if no one had thought of yet (a quick glance turned up nothing on here, but I haven't checked BGG), and in fact, seeing the Inflation post reminded me of it.
Tax
Action - $2
+$2
Trash this card. Put a Tax token on top of a Supply pile.
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During the buy phase, each card costs +$1 per Tax token on its pile.
This is obviously just Embargo with a cost increase instead of a Curse handout. I may be wrong, but I think it should be about as strong as Embargo. A one cost increase often isn't prohibitive, but could make some cards undesirable relative to others, and might make players decide to put more money (virtual or treasure) in their trimmed decks to be able to afford Provinces or Colonies. Unlike Embargo tokens, which are ineffectual once the Curses have run out, Tax tokens seem more permanent. However, like Embargo, they can be circumvented by cards that gain outside the buy phase. I think pricing it at $2 would be correct; after all, like Embargo, a big part of the reason to buy it is just the trash for +$2.
One modification may be preventing it from being applied to Copper to keep those free, but I don't think that's a very serious concern.