97-99 S Class
I would be prepared for LARGE LARGE LARGE repair bills. We are working on a 1996 S500 in our shop right now. The car has 93,000 miles on it and the owner requested new shock absorbers all around, rear air chambers, and front control arm bushings. His bill is going to be around $4000.00 because this car has ADS (adaptive damping system). Each shock absorber costs between $690 and $885. He has already spent over $2000.00 on this car this year, and we haven't even done the 90k service yet.
And be forewarned: while the 97-99's are the most reliable 140's, reliable is a relative term when discussing one of these cars.
I would definitely stay away from the S500, especially one with ADS. The S320 should have suffiecient power and will cost less to maintain, but even with one of these, I would budget between $4000 and $5000 a year in maintenance and repairs if you plan to drive the car from 60,000 miles or so to 100,000 miles or more.
IMHO, a 210 would be a much more economical choice...