I'm in no way trying to stir up something but just because the vet is a vet doesn't mean he knows everything. Certain chemicals which aren't lethal to mammals pose a severe risk to reptiles.
Then instead of using products meant for the specific issue you're dealing with people tend to cut corners then down the road they end up with an issue. I'm not saying you will but it's come up more than once in my 5 years of being a member of this forum.
Bed bugs/scabies isn't snake mites, and the fact you're having to retreat everything again proves that the stuff isn't doing the job it's needed to do. A lot of that stuff only kills stuff on contact, that's not eliminating the eggs and it's not solving your problem. By the time you try all these cheaper methods that are way less effective you would of spent less actually ordering the stuff that's meant to do the job and it would of cost you less from the get go.
While you may even kill the mites on the snake, are you preventing the ones that aren't on the snake that have started crawling around looking for a new host? NO, because nothing you're using is created for that. Mites can go between baseboards, on the walls, up the walls, anywhere you could possibly thing. PAM works by creating a barrier. You have to use the right tools for the job.
That's like if I'm a carpenter and I need to put some nails in the wood, sure I could use a brick, a 2x4, a baseball bat. The fact is that it's not the right tool for the job.
Another example, two pet stores, one clean and the other filthy, well you decide that since the dirtier pet store has rodents $3 cheaper you get from there. Then the next thing you know you end up with a dead snake or a snake with an illness and then you've got an expensive vet bill. All I'm trying to get at is if it were regarding yourself or your children would you cut corners? NO, then why do it for your pets? They rely on you to take care of them because they can't.