BMW's aren't cheap cars. You can use independent BMW mechanics, but the parts are going to be OEM most of the time and it will cost you. Don't buy it if you can't afford it so if this car (which has significant mileage and is the smallest engine) is max of your budget you may want to go in a different direction. Finally, the BMW 320i is coming out and I'm predicting the lease price is going to be very competitive. You could consider a 3 yr lease, get a brand new car, with no concern over repair / service cost. Something to consider.
'07 E90 335i, Cobb Stage 1