Which is why I think the price is right. If they didn't sell them people would be buying multiple copies of the game and transferring the chars to their main account. This makes the price more reasonable than that would be but not so low that you'd never see another char below level 90 again.
Although a better solution would have been to not give people instant 90s at all. But they're hoping to bring back players they've lost over the last few years in WoD but that'd be a lot harder if they had to go through the content they hated so much that they cancelled before getting to the new stuff.