Try Lindsey Bimmerservice in Cedar Park, my GF uses them for everything and they have done very good for now. It can be a bit of a drive but they have a really good shop and the prices are reasonable. I believe "cheap" BMW service doesn't exist and if it did I would steer away. The main guy at Lindsey is a former BMW technician who just wanted his own shop.
www.lindseybimmerservice.com/