If you can't work on the car yourself or have friends who can help you for cheap, get rid of the car. Dealer rates border on outright usury and shops honestly aren't much better unless you get very lucky and find a good one--and even in that best of cases, it will still be very expensive compared to doing the work yourself.
I recommend reading about car maintenance, reading DIYs here and watching youtube car DIYs. Car maintenance is not difficult, trust me. Millions of people around the world with IQs under 100 have done complex and time consuming car repairs themselves by just being patient and following someone else's instructions.
Now, if you ARE WILLING TO TRY working on the car yourself, read this thread to see how you can diagnose any issue the car has yourself for the cost of a laptop you probably already own and an inexpensive ($20) cable:
http://www.e90post.com/forums/showthread.php?t=918608
Then, use this site to find the items you'll figure out need replacing and google the part# to find best prices online:
http://www.bmw.com/com/en/owners/acc...catalogue.html