I bought my rust free '74 duster for $2k. 91k original miles, 3rd owner. /6 but on a '74 it doesn't really matter, numbers matching on anything other than a 360 4 speed is pretty much pointless.
So, you need floors for sure. Tail panel, trunk, parts of the cowl and rockers, plus patches. That's what you know about. That's a probably a good $1k just in sheet metal. If you're paying someone else to fix it, you're well past the $2k mark just in rust repair, no bodywork or paint. And that's if you don't find more rust, which you will, because there is always more rust than you see.
If you're looking at it from strictly a financial standpoint, it's not worth it. You'd be better off finding a cleaner car and parting the one you've got.
Which is not to say your car isn't fixable, it is. Or that you should part your current car, because I hate parting cars. I've seen much worse cars than yours fixed. And it could be a great learning experience if you want to work on a project, and a great opportunity to make your car what you want it to be without worrying about cutting up a "rare" car. But you won't come out money ahead, no matter how you do it.
