Try some rubbing compound / paint restorer first to see if it will come off. Metal cleaning wadding is also abbrasive and good for this (Bluebell, Duraglit, etc.).
If no luck you could try sanding it, masking it and spraying it yourself, if you are any good with a spray can. The BMW orignal spray paint and laquer is only about $20, what do you have to lose?
Worst case get a couple of quotes from a bodyshop, but I think you could be looking well into 3 figures..