Went into Game yesterday and they had Bioshock, the standard edition for the PC, for £12.99. Don't know if this was in their sale or just had its price cut.
Now it's £14.99 online from Game / Gameplay, so you can get quidco on top of that and save yourself a bit extra if you cannot find it instore.
I know this has been posted many times before but this is the current best price for it. I ordered the steel tin edition from Zavvi for £11.99 when it was posted here in May. Well as of today it's still on back order two months after ordered so I gave up waiting for it.
Don't forget they do student discount and hopefully you have some points on your reward card. I got this down to £9.19. :)