they cant charge you if they didnt tell you how much they are. all you have to do if they do charge full price is call your credit card company and tell them they charged you more than you agreed to pay. youll have the order print out to prove it. bank gives you your money back. you keep the goods.
chances are they will just tell you its out of stock and cancle your order.
it is not legal to charge you more than what you agreed to pay without telling you first!!!