Many newer benzes have an aux in port in the glove box it is a mini stereo.
Some do not. it iis just a cable as far as I know.
if you have the nav system, you could get a nav tv unit that will give you aux input and aux video input to the nav system.
If you have the normal radio and do not have the aux in port int he glove box, try holding down the CD changer button for a few seconds. if the unit switches to aux mode, then all you need is a cable, which I believe costs less than $100.00 but am not 100% sure on the price.
I know I have heard of one for the c class from 2006 up I believe that has the newer style radio that is around that price.
Is the mb factory one they have that they want $800.00 for allow you to controlt he ipod via the radio and does it give you text on the screen. if so that is really not too bad of a price all things considered.
But you may want to check
www.densionusa.com and call them on the phone to ask them if they have one for your car. they make a nice unit that works quite well, but they may not have the unit that works in your car yet.
on some of the command units, there is an aux setting that is under the SVC menu under one of the sub menus, and technically all you would need is the cable that plugs into the radio.
on the c class the newer ones 06 - 07 I believe, the plug in for the cable is either behind the passenger side kick panel, or in the cable tray just below the passenger kick panel under the carpet.
Alon