There are good answers on the petrol thread that redcrx posted a link to. A shop does not have to sell you a product at the price that is displayed. By taking a product up to a counter, the customer is offering to buy the product at the price shown, but the seller is within their rights to not accept this offer. A website is basically like a shop window - displaying their goods at a price. A contract is formed when the shop actually accepts your offer of purchasing the item (not to be confused with just confirming your order).
To me, taking your money is a pretty clear sign that they have accepted your order, but there may be some way they can get out of it.
Out of interest.....your link doesn't work for me, what were the cameras priced at? and what should they have been?