That's a bit much, then again I haven't seen the car. I'd start dealing a few grand less.
#1 Maintenance records! They are a must. Stamped books?
With that kind of mileage the upper guide rails/timing chain should have been replaced.
If rear shocks have not been replaced, they will need it. Harsh ride is a sign (it was in my case) and you can try bouncing the rear end. The shocks are expensive, roughly $400/ea.
The rear accumulators will probably need att'n if they aren't relatively new. Not too expensive and is a DIY job. Signs of old accums are also a harsh ride, mine's getting to this point.
A/C function properly? If not, it can cost you upwards of a grand to repair. Evaporator etc.
All the rubber bushings will prob need att'n as well if haven't been replaced. Check for uneven tire wear, front end squeaks etc.
The bottom end is indestructible, top end may need a valve work or at the least, valve guide seals. Watch for smoke at start-up or under load.
If it's been well taken care of, you could easily double the mileage w/o spending an inordinate amount of cash. But like I said, records, records, and more records!
I think my 560SEL gets mid-teens city and a few mpg higher on the hwy. It's been a while since I checked. Best off running hi test, IE 91-94 octane.
Best of luck and try using the search function -- this forum has tons of info and I've merely touched on the main issues. Hopefully some other guys will reply!