I really, really like this. <3
It's probably not all too strong, as i think combining Chancellor and Woodcutter would have been fine for $3 if the cards themselves didn't exist. Obviously they do, but this gives a bonus on buy to make up for the cost. It's far from trivial to decide when you want to use it, though, so if you use it on a card everybody wants, well, it's pretty much no bonus at all. Care to go for a Chancellor-Supported money deck and meanwhile throw some Silvers into your opponent's engine? Or let everyone gain a Copper for your Philosopher's Stone or Counting House? Maybe just gain the last card in a pile? Oh, and the three-piles...
I'm happy
Edit: Oh, i guess Counting House and PS might not be that good with this, considering the fact it can make the game rather short. Hm...