I bought my 87 300D with 159k on the clock. It was absolutley beautiful -- no damage and a near perfect interior. I paid a whopping $6,600 for it when the type was going hot (the other 3 non-private ones for sale I found were all 7K+). The car had an existing shifting problem with culminated with the dealer financing a transmission rebuild. Since then the only major work has been a new radiator.
This car is both a blessing and a curse simultaniously. It's pretty darn fast and handles gorgeously (especially with sportline), comfy, good gas mileage, has just enough technology, and will cruise all day at 120+mph. However, there is ALWAYS a problem with the car, albeit minor some times. It seems like a never-ending cycle, but if you're on top of it and budget a few dollars a month, it's nothing. Then again, I came from a volvo so I really shouldn't talk...
It looks like my head (603-016-14-01 SO CLOSE!) is cracked, but luckily it's not too bad and was much abated with some block sealer. Once I get a new head on, I really don't forsee much of any major work that is predictable for this model, so I'm figuring the last few bits of major maintenance should be it for a while (hopefully).
If you can find a new (preferably 3.5L) headded, transmission rebuilt, cooling system in top notch, no damage, clean examplef or under $6,000 -- I'd say go for it.
Mike