It is NOT a pre-order deposit
No, it is NOT a pre-order reservation cost. According to the receipt I printed this morning when I got in on the deal, it says REG PRICE $59.99, You Save $54.99, Total Price $5.00. The YOU SAVE and TOTAL PRICE figures were just mixed up.
They then add shipping and tax. If you SAVE $54.99 off of a $59.99 item, its cost is only $5.00
This is definitely just a mistake. Whether they honor it or not, will depend on their decision alone. Some industries have to honor price mistakes by law, and others don't. Supermarkets will usually give you one of the item that is wrong for free if you get overcharged from the advertised or posted price. If an item is advertised wrong, disclaimers must be prominently displayed ASAP. I still have not seen a disclaimer about the wrong price on the Best Buy site. They just removed the item so more people can't order it but they haven't notified me yet about any cancellation.