I wish it was closer craigslist finds

If that 70 duster is in fact a provable h code, a 340 and not even numbers matching, rust free and straight (not a complete Bondo wagon..), and a running driver with not too many issues...
In my opinion 15K is a very fair jumping off point... I've seen fully restored Duster h-code go for 35k... 20K of wiggle room to get it to someone's perfect standards is a nice healthy little budget...
Personally I'd probably just change a few things and drive the wheels off it as it is...