I'm always amazed and very envious when I read some posts from people who have no problems in the snow in a BMW. I appreciate that the degree of difficulty depends on the amount of torque and the width of the tyres etc but having spent the last 4 years with an E92 330d on 255s running up a monumental trouser dry cleaning bill, Ive just taken the plunge on winter wheels and tyres for the Z.
As others have said, it doesnt have to cost the earth as Ive just bought a second hand set off ebay for £495. These are the winter wheel package supplied by BMW costing £1600. They have covered 5k miles, have one slight kerbing mark on them and are the same alloys as supplied with my car. Bearing in mind I won't be wearing out my summer tyres throughout the winter, you could view them as being almost free