You'll find that most Thais/foreigners that work/teach in the universities and colleges will have one or two other jobs to supplement their income. One of the prime reasons for working at a prestigious university here is for the contacts - not for the job.

It is through the contacts that you can and will often find very well paying part-time and/or short-term jobs.

B30,000 per month is a very poor wage and you will live poorly on that wage. But - if you use your position to make contacts and secure other work - you can probably double that wage within a year.

You will certainly not be able to support your girlfriend or anyone else on that wage. Yes, some Thais can/could get by on it or even less - but it is their country and culture and what they might find acceptable in terms of living and life standards - you may not. You will find that your Mahidol colleagues will NOT be living on a B30,000 wage regardless of what their base income is at the university.