I thought if you took your old head unit to the stealership with proof of ownership, they'd hook you up with a new one for very little money?

I think you're talking about the BMW business CD radio. Single slot front loader. I forget the part numbers for the models that will work. However, the first thing you want to do is pull the old unit and see if you've got an ISO connector or not. If you don't, you'll be cutting the wiring harness any way you shake a stick at it, and I would recommend just going aftermarket, although that may pose some problems with the stock amp (aka -- open up a whole can of worms).

best, whit