Lots of teachers ARE overpaid, and it doesn't matter if they make 100k or 10K.
The way you know you're over paid is if there are people with your qualifications who will do your job for less money. You're underpaid if there's no one who will do your job for the money you make.
Most private school teachers make less than most public school teachers, so there you go.
The teaching profession artificially restricts competition by forcing otherwise qualified people to go through useless education certification programs. If a school ran like a business you'd pay less for labor and get better results.
So yeah, they're mostly overpaid.
You with the ECON 101 bit again (sorry, outta rep)