Funny you should post this. I was just on the phone earlier with BMW asking about warranties and such. First off to extend the Maintenance to 6 yrs and 100K miles it runs about $2400. You would have to purchase this prior to the 4 yrs 50K mile mark. They also offer an extended warranty and said that they are range from $3000-$4500 with various years and mileage.

Hope this helps?