It's an iffy subject, and you'd either get a good one or a bad one. I spent 2 grand for a rebuilt transmission 2 years ago, and since then it's been an endless string of fixes: new starter motor, solenoid replacements (two faulty ones in a row), and so forth. I only have diesels but I hear that they are easier to work with than gasoline, as long as you have a mechanic who knows how. I'd check that out in your area before you make the purchase.
But: you would have an old mercedes, which might make it worth it. It is for me, but that's not going to convince your wife. If you get one in good shape, and it's your third "emergency" car, it will probably be fine. They are also pretty hardy. My brother's school parking lot flooded and water came through the floorboards and the engine was about two inches deep in water. They towed it out and it fired up just fine. It's got about 300,000 on the odometer, too.