Morning Peter
Welcome to the Forum
I guess your price is from your BMW Dealer ? Not a problem I have ever had to deal with but I did read some time ago about a company "Toponline.com" worth a Google search. Apparently they make roof seals and repair kits. If I recall they are an American based outfit but they seem to have a good reputation
You could also look at specialist dismantlers like Quarry Motors
Good Luck
Dave