I just don't see how you will ever make 50k a month here. Unlike others have suggested, you will most likely not get hired by International schools. A Phd in lit is not a degree in education and those schools that pay well require a teacher's license and 3-5 years home country experience. Teaching younger learners is definitely different that Uni teaching. The other issue is that most will require a 40hour work week eventhough the contact hours might be 18-20.
Uni gigs will pay about 30k for an average of 12-15 contact hours. Some at Chula or assumption make 50+ but they teach extra courses.
I would suggest finding International programs at the University and showcase your ability to teach academic writing or Thesis writing for their Phd programs. If hired abroad, you could easily make 50k. Consultant work pays much better but again you need contacts.
I personally, don't think you will find what you want here. You seem to want the most for the least amount of effort. Without any sort of commitment to the school, you will most likely piss off all your Thai colleagues.