Trade in your old logitech product and get 20% off... BUT! they give you the voucher code before you send them anything. If they do actually make you send something then you can buy a broken mouse from ebay or something..
This makes the Logitech G27 £199.99 delivered which is the best price I can find by around £30.
With 9% cashback from topcashback it works out to be £181!