I used to live in Austin, BensBenz has the most upto date equipment, and is close to downtown, on just before Lamar on 5th. They are a nice group, but are not much cheaper than Continental Cars, which I DO NOT recommened.
I used another place off of Burnett Road, just north of Steck, but way south of 183. They are a much smaller operation, but very friendly, and charge less in most cases.
If I remember the name I will write, but its in the phone book as a Mercedes repair shop