Well if you do go back to looking in the USA then IMO you don't want anything from the east in any case, that's where the majority of the rusty ones will be due to the climate. And plenty of rusty ones come from up Dearborn way too.
Sure there are no doubt plenty of exceptions - cars moved backwards & forwards across the USA for lots of reasons - but my advice & in part from seeing many dozens of Mustangs imported by a friend who was back then in the business of sourcing cars for people - both complete running or dismantled projects - is to stick to the dry states as a car's origin as a best starting point, as he did. We saw plenty of rusty disasters from other parts of the USA imported by people who didn't take that approach. Some were just too far gone to be viable.
Believe me, you do NOT want a rusty old Ford just because it's cheap as you will find that the rust problems go right through all the body shell as there were so many areas that never received any primer at all let alone paint & there was no factory rust protection to the shells whatsoever, they were thrown together in a big hurry due to demand & sent out the door. They are monocoque construction so there are rust traps all through them. They were not hand built with care let alone any thought as to longevity, & certainly not expected to last this long (50 yrs now).
I'm not doubting your skills, perseverance & determination for a moment. But, IMO no matter how good your skills are a rusty shell will take you years to work through, repair properly & correctly for safety, & put all to rights so it drives well, much pain, & many $$$.
Buy a good car to start with & you will be better off & the end point will be in sight that you can look forward to rather than quite some years away.