I had this done twice -- once with a car that had nav in it and another that didn't. The estimates by both dealerships and car stereo shops were the same as yours but overly aggressive. It ended up costing 4 hours of labor at $120/hr for the car that had nav in it, 8.5 hours at $120/hr for the car that didn't. The car should be coded for compatibility as well.

If you don't have NAV already, there are a bunch of other parts that are needed for the installation, including the wiring harness. Expect the other parts to run you at least $1000 if bought from the dealer new.