This is why I'll never own a used BMW.  Even the mundane parts (oil filter, wiper blades, etc.) cost a premium.  And they aren't exactly the most reliable cars outside of warranty either.   
That said, I'd kill to own an M1 with a replica Pro-Car body. (Though, that's really more Lambo than BMW).   
EDIT: Added Bimmer porn: 
http://www.seriouswheels.com/pics-abc/BMW-M1-Group-4-b-fa-lr.jpg