Find another shell. (Note the period)

I started off with an s5 in similar condition. I spent a good 1-200 hours cutting out rust, making a patch panel, welding it in, and grinding the welds. It isn't economical to buy the replacement sheetmetal from Mazda. It was about $600 for just he floor pan from Mazda Motorsports...

I guarantee there are more rusted areas than just the rockers. Look at the wheel wells, the spare tire, the inner frame rails, etc. I gave up and bought a rust free car. It was so nice having a car that could easily be disassembled. Everything was fused solid on my rusted pos.

 

+1.

Imo a car with this sort of damage only gets repaired under two conditions:

-You're a pro, have all the equipment/tools and the experience to utilize them.
-The car is so rare or valuable that money is simply not an issue.

Neither condition seems to be applicable here.

It's especially important to note that extensive repair to a unibody structure is much more difficult and critical than with a body-on-frame setup.

 

seems to me if you're gonna do the repair youself, it's more a matter of investing time than money. Just get the right tools, take the time to fix each panel one at a time, and try and produce something similar in structure to the factory pinchweld by welding all the panels together at the bottom. Use self-etching primer on all bare metal. You'll definitely need more than just a welder tho.

 

my car looks about the same as yours! i plan to repair mine also, hopefully next summer if all goes well. your ideas and the ones given are on the right path. its like therotaryrocket said, just take your time and one step at a time. if your not happy with a weld or a panel just cut it out and try it again, dont leave it. i would not scrap it, if its like mine it looks nicer than most ive seen, unless your under it. mine was given to me because of the rust. i have all the tools and have been helping my dad restore British sports cars for the past 15 years. good luck with it and keep us posted

 

I had it a little worse than you. this is how i fixed it.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s4-2-2-4-bolt-auto-becomes-gtu-big-a55-project-867251/