Peasant, $2
+1 action, +$1
You may discard an estate for +$1
Place a peasant from supply and put it on top of your deck
Setup: place 20 peasants in the supply
Ouch. Essentially this is like buying Coppers that multiply in your deck until the supply is gone. They make your Estates Coppers too, only one at a time at first, but eventually they'll work even if you draw multiples in the same hand. You can get roughly the same effect just by trashing your starting Estates to begin with, which is orders of magnitude faster and less resource-intensive with even light trashers.
Really the only use I see here is for a Gardens or Silk Road rush, for which $4-$5 hands are sufficient, and then only the particular strategy where the piles you drain are Peasants, Estates, and Gardens/Silk Road, presumably in that order. Not sure, but possibly going for these will tip off your opponents, who will contest you for the Gardenses/Silk Roads, in which case you have to race for them
before going for the Estates, which might choke you up too much to finish the race against someone who has not opened his deck up to the Peasant flood.
Anyway, that rush idea IS interesting, but it seems like the sort of thing where, if it works at all, only works one way. And if Peasant comes up in a kingdom without Gardens or Silk Road, then what?
By comparison, note that Secret Chamber offers you everything ANY number of Peasants can, only Secret Chamber earns $1 less (because it doesn't earn a coin for itself) in exchange for providing $1 for ANY card, not just Estates, and any number of them besides. Secret Chamber is terminal, too, but that's not as important since you never need to chain multiple Secret Chambers together, and it can convert dead Action cards into coins.