Take a look inside his mouth. If you see phlegm and foamy spit, that's a sign of an RI.
If he's still wheezing, and doesn't have shed stuck inside his nostrils, I say go with the antibiotics--I would.

I would not pay 400 bucks for the work he wants to do. It's highway robbery. I could get that done here for 200, including the initial visit. I recommend searching AGAIN for a herp vet. Maybe you missed one. If your herp vet has to ask you what kind of snake a ball python is, he isn't a real herp vet, IMO, he's just someone who put up a shingle to treat them, and that can be very dangerous.
I also suggest double-checking his dosages if you get the antibiotics from him. You should be able to find that info online.

I'm sorry you're in that situation--it's less common to find vets who don't know what they are doing treating herps these days, but it still happens. (It used to be the norm!)