I believe in English Common Law the prices in advertising Etc are an 'invitation to treat' the price subject to amendment or negotiation until, the contract is made. For a contract to be made there must be 'consideration' from each side ie each must give someting , the store would give the product and you would give the cost, if there were not cost they could claim no contract, the shipping cost going to the shippers for a separate service.
Let us know what happens.
Let us know what happens.