At the MeilenWerk upstairs that was that company that makes custom car covers. They feel like a wetsuit type material. You might ask around there.
For the cheapest... you might try some of the BMW mail order places on the forums.
http://www.getbmwparts.com/partlocat...catalogid=4462
Also... you should ask Wade what he thinks of the 1M cover. He has one for his car.
e82/e88 out door cover - bmw p/n 82110036863 $185
1M out door cover - bmw p/n 82110038891 $260
IF you look on ebay.de that $185 cover sells for 162 euros. Maybe see what a local BMW can sell one to you for minus the VAT. Shipping this cover won't be cheap(i think).
Dack