This is the cheapest I could find that actually have stock.
Zavvi - £11.66 (inc. Walkers code)
Amazon - £12.90
My Memory £12.95
the hut - £13.44 (inc. Walkers code)
Play - £14.99
Asda Direct - £15.00
Lovefilm - £15.93
bestbuyentertainment - £15.97
Shopto - £17.85
blockbuster - £17.98
Game - £17.99
Gameplay - £17.99
Gamestation - £17.99
Simply Games - £22.85
Argos - £22.99
Everything that made the legendary Street Fighter II a hit in the arcades, living rooms and dormitories across the globe has been brought back in Street Fighter IV. Players will be able to play their favourite classic characters, such as Ryu, Ken, Chun-Li and Guile, along with new characters, including Crimson Viper, Abel, El Fuerte, and Rufus. Characters and environments are rendered in stylised 3D, while the game is played in the classic Street Fighter 2D perspective with additional 3D camera flourishes. Six-button controls for the game return, with a host of new special moves and features integrated into the gameplay system. Street Fighter IV brings a brand new fighting game to fans the world over.
Stylised 3D environments and characters
Traditional "2D" Street Fighter six-button gameplay
Classic Street Fighter characters re-imagined for a new generation of gamers, including the original cast of Street Fighter II
New brawlers: female super-spy Crimson Viper, lucha libre wrestler El Fuerte, mixed martial artist Abel and more!
New special moves that go beyond any Street Fighter fan's wildest imagination, including Focus Attacks, Super Combos, and the revenge-fueled Ultra Combo system
Amazing locations never seen before in a Street Fighter game
New gameplay elements provide challenges for both newcomers as well as the most seasoned Street Fighter pro