as far as I know an advertised price is legally an invitiation to treaty ( it prompts you to offer the sum advertised, the retailer accepts and then you have a contract)
But the retailer has the right to refuse to sell to you
mostly though out of goodwill if they have marked a product incorrectly they tend to honour that sales price, and then fix it quickly so as not to get caught again.
so, to my knowledge, if they refuse to sell at that price, legally you have no grounds to argue. . . .