Nice car.
It's a shame they didn't address the hell hole at the time of the repaint. You clearly got some crud going on down in there under the battery. What it is . . . is very hard to say based on that photo. Looking at the rest of the engine bay, there is a decent chance it's not terrible.
My thought would be leave it alone for a little while. Drive the car. Enjoy it. Save up some money to do it right. Even if you have the money now, I'd still be inclined to drive it before sweating the hell hole which will take it off the road for a bit.
The thing that can answer your underlying concern is to take a screwdriver or awl and poke the sheetmetal that is already rusted (not advising you to scratch up existing paint) down in the hell hole and see if it flexes or begins to poke though. If it is rock solid, get yourself a good AGM battery (no need to conribute to more corrosion with Pb-Acid battery) and drive it. Use a inspection mirror, or your phone on a stick to get a video of that area under the battery that is so hard to see.
If you want another data point, remove the passenger side outer rocker panel and look at the longitudinal. If thre is significant corrosion there, then you know the hell hole is leaking water and/or acid into the long. A solid long will help justify that you don't have a need for an immediate hell hole fix.
When you're ready to attack the hell hole either with a decent sized check and/or time off the road, you won't have a problem finding a shop to do the work.
What you're likely to find a problem with is finding a shop that is only willing to address the hell hole. Personally, I wouldn't do it without a complete engine bay repaint but that's just me. That isn't cheap by the time you pull the engine, and all the little fiddly bits (seals, MPS, hoses, tape lines, electrical, engine compartment lid, grates, etc. No one wants to be responsible for moving your electrical harness around and taping it only to find they cracked two age brittle wires and have now created a short or Fuel injection problems that they are responsible for troubleshooting and fixing. Same if they destroy an age hardened engine seal. Are you paying for that or are they? I'm not a professional paint shop but I can't imagine they would take on the work for less than an 80 hour job. At $100/hr shop rate that is $8k. I can only state that there is no way I could complete what I've outlined in 40 hours so I'd estimate on the high side. What if it went to 120 hours?
I think that is the magnitude of what you're dealing with. Hopefully others join in an challenge me. Maybe I'm overly conservative?