Ok, so I'm meeting the Fire Marshal in like 20 minutes, so I'll learn something there.

Right now the vents/fans have been removed. We've just got patched holes where they once were. The lights are explosion proof. Only a few work right now. That knob is for an "explosion proof heater". It does heat the room well.

We were looking at getting a drop in booth. Numbers around $10k-15k had been tossed out for buying that, which is why the idea of fixing the old booth came up.

My initial, uneducated, thought was to build a positive pressure booth, raise the floor up a foot (or whatever needed) to make a pit and do a downdraft booth that would then vent out the side of the wall. We've even got a high school metal shop (the booth is in the metal shop) that could probably help fab up some of the sheetmetal work that might be needed.

I just need generic ideas of what to research. I really do appreciate that help.

Ok, well the general consensus is that it may in fact be harder to get that room up too code that to just buy a drop in unit. The hard part is finding a place to put a drop in unit. That room is 15ftx27ft and even if a drop in unit would fit in there, I don't know if it would have enough access on every side of it to meet code. ...

I figured it may be too hard to get it up to code, and putting one in that small of an area is not possible they want 3 feet around all walls here in southern Nevada around mine cant imagine your codes are much less maybe 24 inches? but still its not gonna fit it in that room.

Knock down walls?
Or maybe set it up out side of shop, I have seen more than one free standing paint booths set up out side. Works fine Every thing has to be sealed any way.

Booths are a big investment and at that budget don't think possible. You might have to refurbish what you have. You can get away with raising the floor and making it a down draft but it's not a necessary design. You may be possible to make it a cross draft or even a positive pressure booth. Your biggest investment will be to upgrade the fire surpression system that will be a few bucks right there. Can't wait to see what you decide on.

Found a side down draft booth locally with fire suppression for $6k... we would have to put it outside though and it isn't heated. Are heaters possible to install that are explosion proof/etc?

As long as that booth is meant to be outside you can. Yes you can add booth heaters. There are companies that can sell you just a heater.