Or buy the Killing Floor Bundle £6.61:-
Killing Floor Outbreak Character Pack £1.49
Killing Floor: Nightfall Character Pack £0.99
Killing Floor: PostMortem Character Pack £0.99
Killing Floor "London's Finest" Character Pack £0.99
Defence Alliance 2 (Killing Floor Mod) (Free with Killing Floor either way I think)
"Killing Floor is a Co-op Survival Horror FPS set in the devastated cities and countryside of England after a series of cloning experiments for the military goes horribly wrong. You and your friends are members of the military dropped into these locations with a simple mission: Survive long enough to cleanse the area of the failed experiments!"
Not as cheap as before but for anyone who's still interested or missed it previously.. :)