it depends

you need to consider
what fixer upper old road bikes are selling for
these days
in the moutains of north carolina
compared to what recently tuned old road bikes
with new cables tires and brake pads
are selling for

as for appropriate mtbs
your best bet is probably to find something used
from one of the major brands
like trek specialized giant cannondale etc

at your height you probably want a mountain bike
between 18" and 21"

the fit of the bike is the most important consideration