I'm getting the Ipod retrofit done by the dealer on the 9th. He quoted $550 total, including 1 or 1 1/2 hours labor. By the way the parts are only $240 at getbmwparts.com:

65110403651* Each $299.95 $240.00
OEM BMW E70 X5 iPod Interface

The BMW iPod interface allows you to control your tunes through the BMW Multifunction Steering Wheel and stereo system while your iPod sits safely in the glove box, powered by your car battery - which means your hands stay on the wheel and your eyes stay on the road. And unlike with existing cassette and FM transmitter options, sound quality is entirely uncompromised. Just plug your iPod, iPod mini or iPod photo into a special cable installed in the glove box, and you can enjoy endless miles of music pumped right through your BMW's stereo system - with every song at your request. Adapter also charges the iPod's internal battery when the vehicle is running. *Not compatible for vehicles equipped with factory option USB/iPod interface produced from 04/07 - on. Additional parts may be required.

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E70 X5 3.0si Space Grey

E36 Z3 2.5i Roadster, Sterling Gray Metallic