What are some inexpensive ways to hard wire my iPod audio into my 2006 BWM Z4's audio system?

I don’t want to use any kind of adapters you can buy at the apple store because they either suck or won’t work in my situation (no tape player, etc). Someone must have figured out a way to hard wire in an auxiliary jack for around $100—$150. I just want to connect audio only – I don’t need the iPod display to show up on the front panel or any nonsense like that. Who do I call?? The Z4 has a CD changer only.