As an avid merch collector, I would say $5ish for each eraser, and $15-$20 for the Pinwheel keychain. The auctions for them on ebay are outrageous (which is why they haven't sold in months), however, the adult sea pony keychains fetch a high price.
Im sure Sebby and LadyG will poke their heads in to add, as they collect these as well.