Trout, where are you located? That can matter greatly in terms of answering your question.

I'll throw out some hard-won wisdom (I'm 68 and have messed with cars for well over 55 years) - go South and get a rust-free body to start with. If you have to pay a friend to haul it back on his car trailer - still WAY worth it.

Even rust belt cars that seem OK may have significant rust in the structural members (rear jack pockets are a good place to check) and that stuff is always hard to fix. You may have a hard time hiring someone to fix that stuff as, if they're in business, there are liability issues that they simply don't want to get into. I've welded up WAY MORE than my share of rusty hulks (I lived in Michigan for most of my life) and I can assure you that unless you do a full frame-off resto (actually, that's a rotissiary resto on these) they don't stay fixed. So start with a decent body - and shiny paint is NOT an indication of "solid". You have to climb under there and REALLY look and poke. MAACO can make ANYTHING look decent!

The mechanical bits are all fixable though Mercedes can be more challenging than most. I'd start with a late (say, '82/83) 240D with a manual trans. Expect the clutch slave to be bad but these are pretty basic cars and pretty easy to understand. Pelican Parts has provided lots of good stuff for my OM617 (the engine in a 300SD and what I have in my race truck) for reasonable prices (no, I DON'T work for them!).

Have fun!

Dan