Yep the cost of parts is a very big factor for ex. A brake master cylinder for a 325i 88-91 cost $189.95 for an 87-91 m3 cost $254.95 clutch kit 87-91 325i $169.95 M3 $349.95 see the difference!Prices are from www.bmpd.com some places carry them cheaper but this gives an idea of cost difference.But hey,if you own an M3 whats the extra cash gonna hurt?Especially when you've got one of the most prized cars in the world!