Argos are selling the XBOX 360 version for £29.99 or you can get 2 games for £45. I got 2 copies of Call of Duty 4 for £45 (£22.50 each) and traded 1 in at Gamestation and got £28 trade.
They also have PS3 version for £29.99 or 2 for £50.
Gamestation are selling these pre-owned for £37.99 which is madness.
Not sure if this has been posted before, could not find it.