Think I'm screwed

Thought I'd add: I've installed thousands of rivets. It's not fast, it's not easy, it's not cheap. Pop rivets are garbage. Don't even bother. Cherry max are a little better, but far more expensive. Solid rivets are OK, but it's a two man job to install them and it's loud, difficult, and easy to screw up.

I did about 4500 pop rivets in a day using a pneumatic installer. I couldn't even imagine trying to use a hand installer for more than a couple dozen, and you're going to have a few hundred for a floorboard.

If you buy the sheet metal, do some prep and take some measurements you should be able to find a decent body shop to do the install extremely well. A good collision shop will also be able to help you determine exactly how bad all the rust is. Your pictures don't paint an optimistic picture... Expert advise I think will go a long way toward helping you make a decision. For a good inspection, expect to drop $50-100 at the body shop. Maybe more if they spend a few hours..