Along with a title, you need to ensure the Vin on the frame matches the title and tag on the glove box.
Engine, Trans, T-case can be found. Usually the rebuild process (machining and parts) adds up.
Sounds like you have some sheet metal work skills... Having a body shop do the work adds up.
Carefully check the frame over, top and bottom. Check for thining of the metal, The holes for the body mounts can grow in size but are repairable. Over 50 yrs people could have drilled/welded any number of things to the frame, sometimes poorly.
Rust, well everywhere on a Bronco body. Hardtop, tailgate, floors as you have seen, kick panels, bottom of the doors, rocker panels, Engine cowl in the support brace and where it meets the windshield support.
As you know with Mustangs, the little odds and ends really add up in price... Inside and out.
And with body work, the price of materials continues to go up... Rust treatment, primer, paint itself...
But there is no better satisfaction than bringing something back to life, and being able to say I did that! Good luck.