I just had an idea that the overpay mechanic from Guilds could be extended to the purchase of other cards. I am not aware that anyone else came up with this before.
For example:
Village Carpenter
Action
Cost 3$
+1 Card
+1$
-----------------------
While this is in play, when you buy a card,
you may overpay for it. For each $1 you overpaid:
+1 Villager.
Obviously, the important part in this context is below the line.
The on-play effect "+1 Card, +1$" is secondary. I first had "+2 Cards", then "+2$" in mind, but felt that those options are too common, especially in the recent expansion Renaissance. So, "+1 Card" somehow requires some need for +Actions, and +1$ provides a limited economy for overpaying later.
What do you think?