You have to decide what the car is worth to you.
BHD bought a mint 300D a few months ago for $2,800. If he stuck that car on ebay I bet it would go for several thousand more then that.
I paid $500 for my 300SD and it runs and drives very nicely. I know the former owner and he cut the price for me. He probably could have sold it for $1500 it is kind of rusty. But the paint still shines up.
I looked at a clean 1985 300D, for $1,500. It had a few issues, like no power. But overall it was a very solid car and would have made a nice ride with about $1k worth of stuff.
I have seen countless beat trashed MB's as well. Heck I looked at a 300SDL that the owner was asking $6,500 for. I have never seen more rust on a car!
I mean their was not a panal on this car without a few rust holes in it. I could put my fist through the door!
But it had a brand new head, $3k bill.
Prices for old MB's are all over the charts.
I would expect to pay between $1,500-$3k for a nice 300D.