I just took the "leap" two months ago. '92 400e Artic White w/ 76K miles. The car checked out above average. I ran it through a major service "just to be sure". Brakes cost me a bit...had to replace rotors front/back etc...
In the records of the car, the only BIG expense I saw was AC/climate work...blower motor, evaporator and the like...$2K or so.
I am not an expert but here are a few things I have been told to watch:
1 - Power Steering Pump Leaks
2 - Brakes Brakes Brakes...the car loves them
3 - Aux Fans and coolant system
Take care of the coolant system...these babies get hot very quickly if any part of the system is malfunctioning.
Other than that.."perfection!" Just get her serviced regularly, keep fresh oil in her and you should be OK. The car is a blast to drive. It's a lot of fun surprising youngsters in their daddy's acura, lexus, etc...they just think it's their grandma's Benz :-)