I just purchased a 1990 2.6 190E, although it is not luxurious as some other mbs, I am pleased. For me it is a good blend of luxury, sporty-ness, as well as being economical. The 2.3L version I've heard is underpowered, but I can't say I've ever driven one, so I have no first hand knowledge. Like mentioned above, as long as the car has been well maintained, 140k miles shouldn't be a problem. You'll find 190s are fairly common, and replacement parts are relatively easy to find (If you use internet resources)
$4000 sounds like a decent price, if the car were to be in good shape mechanically and asthetically. You might want to visit www.190revolution.net
which is a message board for 190 owners for more information.