Hmm. Well it’s pretty clean and solid overall, it looks like.
One clue or at least something to look at is “how” the rust formed. From the inside out or outside in. With the latter being preferable and less destructive.
Water, Chlorides and mud getting into hard or impossible to reach areas and continuously eating at the metal is more akin to stuff from the rust belt.
A lot of rust on vehicles from kinder gentler areas of the country is the opposite.
Like I found on my truck. Was 100% rust free, chassis and body, save for around the windshield in several areas (and 1 spot under the back window that I didn’t notice until removing the window). I was pretty certain it was water leaking in from the holes in the roof for the visor, when I bought it. And thought what I saw was only the top of the iceberg and figured I’d have to replace large portions of the skin around the windshield.
What I found was it was only rusting from the outside in. Likely from moisture trapped under the window seals. And the corrosion was limited to only the rusted through spots and wasn’t spreading on the back side of the panels.
Likely your case from what you’ve described, or if it was the other way around, a couple holes visible in the running boards would likely only be the start and floor pans, bottoms of fenders etc would also be rotted out or on their way to that.