Having purchased a 94 E420 in October 2000 with right around 100k, I was in your same position. I paid $17,800 before tax and license for the car. Since my purchase, the only significant bill I encountered was for the replacement of the radiator. If you do a search on radiators, you'll see that this is a fairly common item for replacement. Also, I had an oil leak at the front crankshaft seal which was replaced by the dealer at the time of purchase, as well as new front brakes and tires.
Finally, if you did a general search on the E420, you might have picked up on a couple of threads dealing with a check engine light on the 420 motor, wherein the code reads something like "fuel injector open". The commonly quoted fix for this issue is a new computer for the car for $1500+. Obviously, no one with this issue was willing to pay that much, so one of the members swapped out his computer with the exact same model taken from a salvage yard, and he also managed to get a copy of the computer chip from a new computer to place in the salvage yard computer. The check engine light problem is now gone! In fact, I simply replaced the chip in my existing computer with the new chip and my check engine light has not come back on for almost a month. This fix was like finding presents under the tree on Christmas.
In a nutshell, this car gets you pretty close to the vaunted E500 at a fraction of the cost. People do complain about the gearing, which makes the car sluggish from a standstill. However, I have found that manually switching the gears, which allows you to hold on to first gear all the up to redline, produces some very serious acceleration. Given the conservative gearing, it is simply difficult to accelerate quickly AND smoothly when you let the car shift on its own. The engine either stays in the very low revs and shifts very early, or it lunges out of the gate at full throttle. Try shifting it yourself and you will be more than pleased. I asked the dealer whether self-shifting would hurt the transmission, and he said not to worry about it, that it was designed to be driven that way. It is probably easier on the car than simply flooring it every time you pull away from a stoplight, which jerks the transmission around quite a bit in normal driving.
Sorry for the long-winded post. With proper maintenance, there should be no problem with reaching 250K or more before a top end re-build is required. Best of luck.