Mike,
If it is 1986 and newer that you are looking for, then you will have to look long and hard. 1987 was the only post '86 year that Benz put a diesel in a wagon. I may be wrong, but I don't believe they put a diesel in the 210 series wagons. If what I think is true, then 1987 would be it. Prior to 1986, you will have more luck in finding one. Assuming you want a Turbo Diesel engine, your choices are from years 1981-1985 300TD Turbo Diesel. We own one, as well as a 1987 300TD Turbo.
For the price range you're willing to spend, you won't have any problem finding a real nice example.
How familar with MB model jargin are you? The TD after 300 does not stand for turbo diesel. MB did make a model the was a TD but not turbo. The TD stands for touring diesel.
Between 1981-1985 MB only made a little over 24,000 300TD Turbo Diesels. That was for world production, I don't know how many of those were imported to the U.S. Much rarer is the 1987 (124 chassis)300TD. In 1987 MB made only 2,100 (about) 300TD Turbos. That again was for world sales, not just the U.S. MB made the 124 chassis TD for the entire model run (10 years), but only imported it to the US in 1987. I haven't been able to find out just how many were actually imported to the U.S.
If it is bulletproof reliability/longevity and simplicity is what you want then find yourself the best example of a W123 series 300TD Turbo Diesel '81-'85. If you want the fastest, smoothest running diesel there was, try and find a 1987 300TD. Be sure to see if head has been worked. These eninges had cast iron blocks and aluminum heads. If the enigne ever got hot, the head would develope cracks. Be warned, once you drive one of these you will be hooked.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member