This is a wild guess, but I am going to say $600 or so from a dealer.

If you want just a "major" service done to the car, look at the 60k mile service in the book. This should include an oil and filter change, engine air filter change, spark plug change, cabin filter change, fuel filter change, wiper blades, and checking the condition of a few components as well as leak checks on the car. Probably a few more minor items on the lost as well.

Add a coolant change and brake fluid change if you think its been a long time since those have been done.

If you are handy, you can do the job yourself for less than $200 worth of parts.

Hope this helps. 12 MPG seems a little low, is that in a lot of traffic?

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record