Did someone type in the price incorrectly? I suppose it was that, since it's only BitStamp that's this high. BTC-E is at $481.
BTC-E is always 10-11$ cheaper. I don't know why.
Btc-e is not really cheaper. Try depositing funds. You have to use 3rd party deposit methods that charge 1% fees. So btc-e is a little down (imo) because of those additional fees.