I love the E-Class Mercedes. The 300 series is the summit of the evolution of the original 190E class.
I recommend the 1991 300E to you. You will find it an active and versitile Benz, capable of hurling you at incredible speeds - all day.
With 140K on the clock - look for the following possible trouble spots:
* Use of oil over time (about a quart every 1500 miles) - ask the current owner - this is a sign of wear in the valve train (guides and seals - note - there will likely be NO smoke - no matter when you start the car) It's is not a large problem - and for the cost of the quart of oil over the cost of a valve job - well....pay for the oil.
* Check the drivers door lock. See that as you activate the factory secutiry system (by locking the door) that you can unlock the door - in you normal fashion - and the the system will disarm. Sometimes the drivers door lock barrel contacts become dirty or worn - and the disarm/alarm (by unlocking the door) is slow - so you have to put the key in again and twist it in the "unlock" direction again.
* Check all other "usual" points on a used car. E.g., ball joints, shocks/struts (for leaks), oil leaks (falling on pan under the engine), Air conditioner, play in the steerting assembly (should not be more than 3/4 inches (MAX!), etc...
For the price - it's sounds nice - but do your homework (now that you know what to look for in the car) - and maybe you can get the price further reduced!
Best of luck!
1991 300E (Autobahn Modified)
1986 Trans Am (Race Modified)