Al...I have a 65 coupe. About 4 years ago I contracted with a shop to have the upper windshied frame replaced. It was completely rusted out on the RH side. Rest of the frame and birdcage was in great shape. Coat at that time was $2445. Took 37.5 hr. labor plus parts. I considered that a bit pricey but after seeing what it involved and the expertise it took it was worth the money. I wouldn't of tried that on my own. Anyway, maybe that will give you an idea of the cost and what you may be getting into if you find more rust problems. Best of luck to you.
Bill
Bill