Was on "sale" for £20.09 or something on Steam a few days ago. This is the Steamworks edition, so you're getting the exact same thing in a retail box.
Not bad for a three month old game! 76 on Metacritic, although some have slated it for not being an "old-school" RTS.
Quidco as well.
Edit: apparently the game is getting free DLC this month too.