In my opinion, it all boils down to what you plan to spend, and how much you can do yourself. I agree with others that your estimate is WAY short. Mine wasn't near that bad, but I'm not a metal work guy, so I had to pay someone to put my body back together. I have sentimental value in the car (first car I ever bought myself back in '87) or I would have NEVER done it.
I have approximately $8K into AMD metal and over $15K into labor just to get to where it is in the pictures below. Count on there being twice the rust that you can't see than there is that you CAN see.
Your estimate of $30-40K will only get you about halfway done. If this tells you anything,.... not counting the big ticket items like motor ($3-5K min), trans ($1-2K Min), glass ($1K), interior ($4-5K),.... I went through an excel sheet I got from 69bfan on here and all the little stuff I need added up to another $6500 for things like weather-stripping, door handles, interior latches, arm rest frames and pads, mirrors, etc etc etc.... It's easy to say you have all those little things, but once you have nice pretty new paint on there, it's amazing how all those things suddenly look like crap next to that new paint.
Trust the guys on here,..... You are biting off a HUGE project with this one that will cost WAY more than what you are estimating, and WAY more than what it will be worth. You have to decide for yourself, but please go into it knowing this could (and will) turn into a HUGE money pit.
Not a pessimist,... just honest after looking at all the costs piling up on mine!!

Hindsight being 20/20,... I would look for a MUCH cleaner starting point that you can tinker with to finish out and enjoy.
