[Howdy, I did some cleaning up on this thread.]
If I assume you're selling them online like ebay, take a look at other seller's auctions there.
I looked at just a couple plushies where starting bids ranged in $15-$30. What you really can get depends on what anyone's willing to bid or pay for even the rarest of plushies.
Now, you were asking for advice, so please don't post about actual auctions or sales on the forums for that is considered spam.
Why Brain? What do we want to do tomorrow night? Throw a slumber party?