A couple of points here:
Firstly, being qualified to teach English in your home country does NOT qualify you to teach English as a foreign LANGUAGE to non native speakers. To employ a PGCE qualified English teacher from the UK in a Thai classroom, who has spent his/her career teaching Shakespeare to UK teens, would be akin to asking a doctor to remove your wisdom teeth.
Secondly, qualified EFL teachers at the likes of the British Council earn around THB 85,000 a month. They also receive a generous benefits package including return flights, health insurance, all visas covered and a minimum of 35 days a year paid holidays. IDP and a few others offer similar packages albeit round about the 60k mark.
Like most industries, what you earn depends on what you're able to offer.