Well, it sounds like it is likely a good buy. A well maintained mercedes diesel will last a very long time, and as such the mileage would not scare me. Heck, even my dodge is in that neighborhood and runs great! Now without seeing the reciepts and knowing what work was done, I would have to guess that the car has been well maintained just because they kept records and the car looks good. If the transmission is an automatic, I might be concerned about the mileage (check the records). If is a stick, the only thing I would question is the clutch. At a price half of your budget for purchase, you still have room to play with for repairs that might not even be needed.
As for whether you should hold out for another car, only you can answer that. It sounds as though higher performance is not an issue. If that is the case, the simplicity and reliability of the 240D should not disappoint.
\'87 Mer-B 300D (220,000 miles) (sold)
\'93 Mer-B 300D (173,000 miles) (sold)
\'87 Porsche 928 (101,000 miles)
\'98 Dodge Ram quad-cab (250,000 miles)
\'2001 CLK430 Cabrio (50,000 miles)
Past cars: 1969 mercedes 250, 1981 300D, 1972 220D