Maybe I'm missing something, but unless you're running with the super low priced Battlechest+MoP deal they had around New Years I end up with $20+$40+$25; that is what it would take to buy the Battlechest, the expansion, and then transfer your level 90 across accounts. A $50-60 level 90 doesn't seem far fetched to me, since it will make the decision to purchase weighty enough that people won't just fill their character slots with 0 game time played, but at a price that is still a better deal and easier than buying an expansion for an account you're going to burn afterwards.