A cursory look seems to indicate the Blizzak LM-32 RFTs are around £115 a piece so a set of four comes in around £460 (incl tax & delivery), although might be able to do a deal for four. On BMW pricing that leaves £448 to cover a set of 16" steel wheels, fitting and balancing.
Have a sneaky feeling that BMW charge extra for storage - quoted price is £30 but I'd be surprised if you couldn't negotiate that down to 'free'
