Alien-blasting FPS Prey should be available to purchase from Steam today. $49.95 is the price to pay. Anyone who has previously bought retail or download editions of the game can "activate a copy on Steam at no cost by using their existing product key", is the word on the Steam website.
Powered by the Doom 3 engine, Prey follows the plight of Cherokee garage mechanic Tommy as he battles alien aggressors in an attempt to save his skin, his missus and planet Earth itself. Tommy's extraterrestrial adventure begins when he's abducted onto an alien mothership orbiting our world.