I'm doing a unibody rust repair on a '70 e that I used to own for the new owner. I have history with both the car and buyer and it means a lot for the car to be finished right, and that the owner not be dissapointed with anything. So he's getting a huge deal on labor. But - materials and paint will run close to $8K when it's all said and done without an ounc of labor. So as to you question the guys nailed it:
You can't possibly know what it needs until you actually start taking the visually rusted parts off. I feel it's pretty safe to say it will need 30% more in terms of parts and labor than what you can easilly see when the car has been stripped to the unibody - and some of that needs to be fabricated or come froma parts car.
Money wise - if you can do it yourself you'll be happier. But - the best repro parts are still not factory. You have to be good enough to know what to look for and how to address issues that will creep up with the new parts and you'll need an environment to do it, and the tools and equipment to do it. So how much are you really saving?
Lastly in terms of materials parts, labor, and paint - you get what you pay for.