Adding an IRiver MP3 Player with Audi Symphony II?

[brunop]

I've got an IRiver H340 mp3 player and want to attach it to my Audi with Symphony II stereo. I understand that I need some kind of AUX input but all the ones I can find are £50 - £70. I can understand that sort of price to add a CD Changer as I guess there is some electronics going on to provide power and control to the changer, but to add an mp3 player just as a line-in device (no power or control needed from the Symphony) surely this can't be right? Am I missing something?

Any ideas or recommendations would be great.