I just had the module installed last month in Los Angeles... $400 for the part and the install (tax included). When I first called they wanted $690. So I called around to other dealerships... prices were all over the map (from 400-800). Went back to my dealership and finally convinced them they should be doing it for the price of the cheaper quote which they did.
The module sounds great. So much better than listening through the FM frequency... but skip the direct connection and use the RCA cable input. Navigation through the stereo is a mess. Better to just use the RCA jacks and interface directly through the iPod. You lose the charging capability this way but it's a small sacrifice.