Are we talking a real international school or one of the many calling themselves such when they in fact aren't? A real international school would be paying you so much that you wouldn't bother questioning the conditions of your employment.
Depends what you're carrying too. And if Border Control show is wandering around looking for a story, Not so great if your father is waiting outside arrivals to get you. Then chances are when the officers see in the computer what they did last time, they will do the same again. I wouldn't advise overstay even now.
The issue was that I spent 2 hours having everything inspected and xrayed, while the officer read nearly every word of 3 older travelling diaries I was carrying. The xray machine damaged a sandal wood statue. You don't give Australian immigration a reason to pull you aside.
$US1000 a month with living expenses on top would make Thailand an expensive country to live in if free basic medical care is available in your home country.
One thing not mentioned about overstay is the reaction of immigration in your own country upon return. The overstay will be noted in your passport. I unavoidably overstayed several days some years back and spent over 2 hours being inspected, searched and questioned by immigration officers back home. It's not an experience I wish to repeat.
I went for an expensive cover covid that includes ( I just had covid and am dead scared of getting it while OS on a visa exempt 30 days), both medical and trip disruption, as well as cover for a known medical condition and motor bike riding. Also has real people manning phones rather than email communication only. It was with Fast Cover, but if I wasn't turning 70 while away and feeling paranoid after going nowhere for 5 years, I'd have gone for a cheaper cover - 1cover or maybe something like Tick.
For a 30 day stay only, I would imagine the airport deals are about as good as you're going to get if you need a phone for immediate use on exiting the airport. It's a bit inconvenient having 1gb for only 24 hours then having to negotiate a short term plan.