I drove a 300d turbodiesel once, and had a '77 280 se for a couple of years. The 240d will get a ton better mpg than the 300td wagon or the 300sd sedan. The 240d non turbo is easy to work on, and you can get about 30-35mpg normal driving. a 300d, 300td or 300sd will get tops 25mpg with normal driving. the 240d is really slow, but without a turbo that is one less thing to worry about. If you can deal with over 20 seconds 0-60 time then go for it. If you can work on the car, it'll be great, otherwise set a thousand or more aside for upkeep. The w123 240d is very easy to get parts for, and a parts car would likewise be an affordable side option. I turned down a cherry, rust free '74 240d for $500 a year ago and deeply regret it.
ps-try to get a manual, the autos are dreadfully slow. This is especially true with the 240d, since you'd have no turbo to help you along. You may have to replace the clutch, but a mb auto will shift really sloppy, and not last nearly as long. If you do the valve adjustments on the engine every year or so, the engine should last a long time. You can even upgrade to the pencil type glow plugs that will start the car much better in the cold. Mb's supposedly can run on veggie w/o any sort of conversion, i never did it, but I met someone who does with no problems at a fairly potent mix of veggie to fossil.
I had my 280se b4 i worked on cars, and I spent about 1500 over the first year. This included tie rods, exhaust leak, tires, alternator, battery, and brake discs/pads/caliper rebuilds. All easy stuff.
My mechanic has a woman who got a 1970's Diesel Benz wagon for possible conversion to biodiesel. My mechanic warned her before she bought it that they cost *alot* to maintain and the parts are hard to find.
Soooo, like budomove said, you need to be able to do some of the work yourself in order to make it economically viable for you.
now that I think of it I think it was about 2k in upkeep over the 1st year, and the auto trans was acting up at 145k miles. It was almost worth the feeling of security, but not quite. Like Carlos says, it'd be great to not have to pay all the labor costs of maintaining one of these cars.
I have an 85 300td wagon. It is the last year for that style of car (and engine?). Anyways, I roughly track my FE buy filling up when on E and resetting the trip meter. I get about 400 miles on a 16 gallon fillup, which works out to about 25 MPG. The only things I do to try to improve FE is keeping the tires inflated and by gentle acceleration and coasting (ingear, engine on) to stops.
Don't let anyone scare you about buying one of these cars. They built 2.6 million of these cars in various styles over the years. Parts are cheap and easy to find, plus you won't need many parts anyway because they don't breakdown. These cars are like those hundred year old foot pedal sewing machines that still work just as good today as they did when new. They were built with a different attitude than todays disposable cars.
When I get to talking with people about the car I say that this will be the last ICE car that I will own, my next car will be an electric. They usually don't get it. What I am saying is that by the time I need a new car in maybe 15 or 20 years, I suspect that there will be a good selection of electric cars in production and I will buy one of those.
I've got a '71 220D (with a manual trans ) It is a great car, but I wouldn't reccomend these cars as a choice strictly for economy. Back when diesel cost less than gas it was true, but the price reversal thesedays has done that in. OTOH, the car is a pleasure to drive.
I drove the car from Va to Id and got a steady 35mpg at 60mph on the interstate. Driving on my usual route with hilly highway miles I get 30mpg doing the same 60 except where the car can't keep up that speed on hills. My LeBaron gets 27-28mpg on regular gas doing the same route at 65mph and it doesn't have to slow down for hills. Compare the cost of diesel to regular gas and the cost per mile doesn't fall in favor of the Benz.
The car really doesn't want to go much faster than 60 that for long periods. With the gearing, it is doing 3000rpm at 60, which is ALOT for a diesel! It is geared the way it is because it only has 69hp in a 3000lb car and needs the gear advantage. 0-60 is in the 20-30 sec range and top speed is about 75mph on level ground.
Whatever mechanic said parts are hard to find is full of it. At the least you can go to the dealership where MB does still have every part available. That is not the cheapest option for sure, but as a last resort the parts ARE available.
My girlfriend's mother drives a '99 or '00 E300 TD. Drives like a champ on the highway (40mpg+ is easily done) but costs a fortune to maintain. It would be less expensive if she weren't taking it to the dealer. On the other hand, it has something like 140,000mi on it now and the only major problem outside of normal maintainance was the high pressure injection pump failing at about 130k.