even if it was in perfect shape, 340 darts are not worth all that much to be honest... even numbers matching perfect resto.
their value is the performance fun to drive fun project.
definitely will cost you some good cash for the project. more than what you can sell for after. it's more a labor of love than a profit venture.
that being said, you could probably get it for 1500 cash. it probably has a 318 or 360 sitting in it, but you never know. things to check for - frame rusted through, that will be a major repair. also if you do get it make sure you get all the spare stuff he has going with it. some stuff is really hard to find.
but plan $5k-6K into an engine, probably 2000 in body parts, money or skills to install those body parts. (can you weld?) . $$$ for paint, paint job or skills to paint. stuff like that. it helps if you have buddies and a little network goin of people that love working on cars. suspension parts. odds n ends. interior work. etc.