ShopTo are selling Dark Sector for the Xbox 360 and Sony PS3 for £22.99 (inc Del)
You can get cashback through the usual sites (e.g. 5% Quidco, making them £21.84 each)
The next best price for both is £24.93 from The Hut.
Dark Sector thrusts players into the role of Hayden Tenno, an operative sent on a dangerous assassination mission into Lasria - an Eastern European city on the brink of ruin that hides a deadly Cold War secret. Attacked by an unknown enemy, he awakens to find part of his body altered by an infection that has granted him inhuman abilities. Now, Hayden must learn to evolve along with his powers, to survive and to become a hero.
Created by acclaimed developer Digital Extremes, Dark Sector is a new and original action-thriller designed exclusively for next-generation consoles. A dark, gritty experience packed with fast action, incredible superpowers and an engaging story; Dark Sector represents the next evolution of action gaming.