PeaceBlondie

For all practical purposes in the EFL profession in Thailand, there is absolutely no correlation between the salaries of Thai and foreigner teachers. None.

A. The farang is not Thai, not a govt. officer, not a native speaker of Thai language.
B. The farang is not a Thai citizen, and total annual expenses for visas may easily run 84,000 per year (averaging 7,000 baht per month).
C. The farang has no family here, no support network. If he wishes to see family, the 84,000 in part B may run to 108,000 per year (9,000/month).
D. Most farang are illegal workers, like Burmese street cleaners. Even with proper degree, they probably don't have work permit, proper visa, no permanent residency, etc.
E. They have a skill that 99% of the Thai EFL teachers will never have: native fluency in English. That alone puts them in a totally different labor pool or job market.
F. The farang get no pension, limited health insurance, no line of credit, no ability to own land or house in their own name, etc.

The salary of a Thai ajarn, school director, or prime minister have nothing at all to do with the day wages of a street sweeper, or a farang who teaches in native English. If the only two qualified farang who are willing to teach math or science in Udon Suckathai both want 85,000 baht per month, that is the prevailing wage, and the only supply.

__________________
"The times I've been mistaken, it's impossible to say" - by the Moody Blues