Blizzard doesn't itemize "World of Warcraft," but free-to-play MMO "Perfect World International," a game that's grown to over a million users in North America alone since its open beta last September, had players willing to pay the price of a full retail game for an extremely rare mount.
People are willing to pay more than you might think to be unique online.
"Perfect World International" was able to charge $50 for a giant snake mount called "Ancient Boa." A mount is an MMO term that refers to a creature you can ride. "Ancient Boa" was only available for two weeks in "Perfect World."
But people paid. "Perfect World" is otherwise free-to-play, however. Unlike traditional MMOs in North America and Europe that work on a month-to-month subscription model, "Perfect World" charges nothing for access to its content, instead relying on players purchasing convenience items and costumes.
Put yourself in their shoes, "World of Warcraft" players. Would you pay $50 to be unique?