I paid $225 including parts and labor for installing the Auxiliary Audio input in my 645ci on February 2005. For parts and labor to install the Auxiliary Audio Ipnput in my '06 M5 I paid $182 a year latter on Februaty 2006.
The price you were quoted must be the California labor costs, since I live in Alabama.
'06 750Li, Black Sapphire Metallic
'06 M5, Black Sapphire Metallic, Sepang Bronze Extended Leather, SMG, Heads-up Display, Premium Sound
'05 Silver Gray Metallic 645ci, Hamman Aerodinamic Mods, M6 Wheels, Brembo Grand Turismo brakes
'03 325i Dinan Stage 2 Mods, M3 wheels