if you have oem 18's just order winter tires for those. if you don't have 18's, look for used oem 18" wheels for sale right here on M3 post. its going to be much cheaper even with shipping than buying a set from a local BMW center here in Germany. for tires, I have a tire guy local that usually manages to beat tirerack and mount/balance is free. not sure where you are located though. i'm sure there is a local guy in your area that will do the same thing. just start with pricing out tires on tirerack.
"It gave you amazing satisfaction, but anyone who says he loved it is either a liar or he wasn't going fast enough." - Jackie Stewart on racing at the Nurburgring