i read a post that it cost someone $2200 at the dealer for Alternator Replacement.

it cost me 400 (370+tax) for the rebuilt alt (anderson auto electric in waterbury CT. They do drive shafts and differentials too - this guy hooked me up nice and Quick!)
two new belts (52K miles on the original) (60 bucks from BMW)
a
gallon of antifreeze (20 + 1.50 for distilled water)
8.5 Quarts of Mobil 1 (about $6 a quart)
New Oil Filter and Drain plug (15 a la BMW)
New Air Filter ($15, this should hold me off for awhile. i want put on an intake)

that's a total of just under $600 or so. (including gas and such for driving around gettin the parts. I havent sold my 2005 Ford Ranger yet. So i got a rebuilt Alt, belts, I got an oil change in and new coolant. I learned alot about BMW's and Didn't break anything else in the process of working on the Truck - So yes it was worth it. If i broke something i would have cried, or if i put it back togather and she blew up, i would have fainted then woke up and cried.