So -$1 is probably not right. Or maybe $5 is not the right cost. But I like the idea of changing what cards are available to buy during the game. How about this:
$4 Action
+$1
Trash this card. If you bought an action card this turn, remove the remaining supply of that action card and replace it with a supply of equal number from the randomizer set.
The randomizer set would be face down and you would replace it with whatever card was on top. In the instance of it being a victory card, you would replace it with the full number available for that game, regardless of how many cards were in the pile that was replaced. I fully realize that this is probably swingy and hard to implement IRL. But, again, I like the idea of changing the kingdom in mid game, and if there is a more optimal way to implement this idea that will still be *balanced*, I'd be stoked to hear ideas.
But maybe this is a boring idea to everybody but me.