What is your objective with the car?
1. Full restore; you will end up with a great car, but be 30-50k in the red. My car looked like this when I bought it, and it had a lot of rust surprises. I did a lot of the work myself, but I farmed out (1) blast and epoxy paint the frame ($250), (2) repair and repaint the body (10k - cheap, the shop used my car to reduce losses during slow times... i.e. if there is no work, but you're paying the crew, they would work on my car. It took three years.) (3) Engine rebuild (~5k). Parts costs, while "only $100" each, add up fast!
2. A partial restore. The sheet metal looks good (from the photos). You could disassemble, buy a new Ratco frame (~3-5k??), por-15 the rusty floors, and put it back together. Figure 10k total investment, but can easily creep up... once you're at it, may as well redo the seats... then the interior carpet... jeez once I spent all this I may as well repaint the car... See #1 above.
3. A car that you will work on as-needed. For example, weld on some patch panels on the frame where needed (assuming you can get to them without removing the body), apply POR-15 to the floors and other rusty bits, covered with rattle-can paint. Maybe patch in some sheet metal if the metal is perforated. Some parts may look funny, but hey, who cares - we're enjoying ice cream at the Saturday Night Cruise!
4. A car in good condition that you just want to drive the day you buy it.
If it is #4 you are after, my gut tells me this is not the right car. Elliot's details suggest there is more rust lurking in other areas. Do you like metal work? It's not hard, but messy and a little tool investment ($) goes a long way.
(Counter-point: buy it, do nothing, drive it like you stole it, and when it falls out from under you due to rust, just remember the smiles you had, sell the engine, tranny, and any other useful bits, and carry on with the next adventure.)
Regardless, should you buy the car, I would suggest replacing (or very closely inspecting) all the safety bits: Flexible brake lines, brake fluids, tires, etc. Not expensive - significantly cheaper than extracting a nose from the steering wheel

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