Or you could buy the AudioLink adapter ($125) and an iPod ($150-250). A 30GB iPod is only $250 and it saves you swapping CDs all the time (since even 6CDs is only about 4GB.
I got an 80 gig mp3 player but it's a pain in the ass for short rides. I have a XM Pioneer Inno too which is quicker to boot up but I miss the mp3 discs that I made for my old car that supported them.