Like $2K at the most
Theres a 83 240D I see on CL right now. Guy wants $1850. Called him and he says it starts up fine and only needs to be plugged in in the dead of winter. Said a/c "just needs a charge" but I dont use a/c even when I drive my parents newer cars.

Said hes getting rid of it b/c his wife just got a newer jetta
Might look more into that one
If its something minor on the 300SD though, I cant bring myself to pay as much for a 240 as I would a 300 with a turbo

http://stlouis.craigslist.org/car/382667003.html