I just came across this aftermarket system from Bimmian.
Looks pretty reasonable for the money - $500. I know that the Garmin has a lot more to offer but is about double the price. I would probably only use the nav a few times a year at most - thats why I didn't want it as an original option.
Interested in your opinions.

http://www.bimmian.com/GPS/AA/froogl...40fd311cfdc5e2