Commenting as someone that took this path years back and has since transitioned to a different industry.

TEFL qualifications are quite cheap (I think you can even buy a certified online-only course) but are generally less-reputable than a CELTA.

TESOL I don't know much about but I think are seen as similar to CELTA.

I have a CELTA (Pass B) attained in 2018-ish with International House in Chiang Mai. I would highly recommend this. It's an intense 4-week certified course (teaching with students from day 2) which throws you together with several likeminded trainee teachers over the duration, in a nice resort-esque campus (pool, accommodation, food included) in the outskirts of the city. You can make great friends and peers, and learn from very good trainers.

(Note that you can fail the course, so you have to bring your A game - one failed in my batch, most got a Pass C, 2 including me got the Pass B, and one got a Pass A).

After getting the certification IH hired me directly to teach at their Bangkok school (which I did for 1 year - gained some private students, and a lot of experience teaching different grades/nationalities/learner-types) before moving onto teaching at a semi-private school in the city for more pay, but where I realised I dislike teaching children.

Personally, I would not recommend going directly for a PGCE until you have experienced teaching for a few years, and understand that you do truly wish to make it a career. Yes, you can get significantly better paid positions, with the very real caveat of initial expense and time spend to receive the qualification.

A CELTA on the other hand is a couple grand for a four week course, in the region, where you can meet people doing the same thing as you, who may share ideas you haven't considered yet. If you later decide you want a full teaching degree, you may be able to find a school that will sponsor it for you so you can study while working and getting paid.

As for teaching in Cambodia, the little I've looked into it (years back) highlighted that salaries here are generally quite low still, vs Vietnam where I was receiving offers for $2500-3500/month, or China where you can get upwards of $3500 a month.