ChoicesUK is selling "Marvel Ultimate Alliance" for the Sony PS3 for £14.99 (inc Del.)
You can get cashback through the usual sites (e.g. 5% Quidco, making it just £14.24)
The next best price seems to be £17.93 from TheHut.
Marvel: Ultimate Alliance is an all-new action/RPG where players create their Marvel dream team from the largest roster of Super Heroes ever in an epic quest that will determine the fate of Earth and the Marvel universe. For decades, Earth’s Super Heroes have opposed evil in their own cities, and on their own terms. But now, Dr. Doom and a newly reformed Masters of Evil – the greatest collection of Super Villains ever assembled – have plans for world domination, and the heroes must band together to defeat them. Playing as some of the most revered Marvel characters, gamers will embark on a dangerous journey across exotic terrain and well-known comic book locations like Atlantis, the Shield Heli-Carrier and the Skrull home world in an attempt to defy the world’s most notorious Super Villains. Created by Raven Software, Marvel: Ultimate Alliance lets players control the most powerful Super Hero alliance the world has ever known.