I bought New Super Mario yesterday in HMV for the full price of £32.99, but there was an deal if you traded in Mario Kart, you could get it for £5.99 which sounds pretty good.
You could maybe pick up Mario Kart for £20ish online so basically New Super Mario Bros for about £25.
I think there's another deal posted for GAME which is trade in Mario Party 8, Mario Kart, Animal Crossing etc and get it for £14.99 so this works out better.
There's no mention on the website, in store only.
Ends 26th November.