Cheapest by some margin for the full band bundle which consists of
Guitar Hero 6 Warriors Of Rock Game
or you can choose the guitar and game or just the game, here is a summary of prices with free delivery. Stand out buys seems to be the PS3 for the full bundle at £60. Guitar & Game on the 360 at £30 and for the game only the PS3 at £9.10.
Full Band Bundle - Wii £59.99 PS3 £60.00 Xbox 360 £69.99
Guitar Bundle - Wii £42.99 PS3 £34.99 Xbox 360 £30.00
Game Only - Wii £17.47 PS3 £9.10 Xbox 360 £14.99
I hope this help's someone.