I have used several of the products from Dension including the Gateway 300, Five and Blue. For your car they list the Gateway 500. This device is around $450, plus another $150 if you want to do bluetooth. The ipod cable tends to be extra as well, though I don't remember how much. Note that there are some caveats for your car, see their compatibility page for the Gateway 500.
These devices will also play audio off USB mass storage devices. That's mostly what I use them for, though recently I upgraded to one that will do Bluetooth phone audio and music.
Their products are solid, in general though for playing USB it requires a Windows program to generate an index for the music to get the full functionality. Their products are also kind of all over the map, for example the 300 I started with worked very reliably. The more recently introduced Five requires steering-wheel audio controls, which my car does not have. They wouldn't answer me about why they didn't make it so that you could use the head unit controls like the 300 does. So I switched to the Blue, which doesn't require the steering wheel controls, but also doesn't display song titles on the car displays like the 300 and Five do -- again for no reason I could figure out.
Another option I have heard of is from Mobridge. I have never used these units, but my installer is in love with them (they need to get a room :-). However, these are quite a bit more expensive than the Dension units, from what I could see, around 50% more.
I have purchased the Dension gear from Enfig Car Stereo, and have been happy with them. I found them by using the Dension compatibility matrix to look up the exact product code I needed, and then putting that into google and clicking on the "Shopping" section to find vendors.
Disclaimer: I have no relation to the above companies except as a consumer of their goods.
