Sad shape = big bucks. I lucked out big time in about 1993. Answered a local Chicago ad for a non-running Cali. original '70 Mach 1. Turns out the owner had ittrucked from Belmont, Cali's high desert to a noted Racine, WI rod shop where it sat for a year in a big barn. Metal was in great shape and the car had a nice red repaint job late in its Cali. stay. Bought it for $5,500 cash as he was getting divorced. The price included the shop's own enclosed car hauler delivering it and all the parts 90 miles south to my suburban Chicago home!
Long story short I junked the blown 351C, auto trans, A/C, power steering, the entire interior save the back seat and side 'glass panels. New glass, engine, trans, rear pumpkin, total Boss 302 racing suspension, Shelby drop, grille, honeycomb rear panel and more. Even though it came with boxes of parts, many were old or worn. $17,500 later it ran and is still running today.
If his is rusty, good luck with the rebuild as it won't be cheap.