Lorinzo, it really varies from shop to shop. Your rapport may play a role in getting installation costs down. One thing I can tell you for sure: Do not have a dealership install it. From my experience, they charge WAY more than what a reputable shop can do competently an charge. European Auto Source in Anaheim is my preferred shop for simple bolt-on installations. For the more involved work and fabrications, I'd go to LTBMW in El Monte.
Parting out my car. Please visit my Facebook
to see list of available items and some photos. Additional photos of my build can be found on European Auto Source's site, here