Weatherproof sockets

Ill soon be doing up the garden and am looking for a rough quote for a weatherproof double socket in my back garden. There's a spur for the washing maching on the inside of the wall and other sockets on the wall above the countertop. Its a newbuild house, specifically a persimmon portree Id prefer the sockets to be fixed to the wall rather than hung on with a screw with no wires showing.