The lowest price progressives I could find in Bangkok: cheap frames and non-brand lenses were B15,000 at a shop in Pratunam 5 years ago.
Vision testing in local shops is not trustworthy as well in that there are no licensing or training standards...any shop employee gives vision tests.
I get my vision tested at Rutnin eye Hospital every 3 years, now about B2000. If you go, be sure to request a "VISION TEST" and not an "EYE EXAM" as an eye exam is a physical eye examination and usually does not include a vision test or prescription. Make sure your prescription includes your "pupilary distance" (PD) required for progressive lenses.
As BritMan2 suggested, Zenni Optical (Yes, Chinese and very excellent service and quality) My last pair 3 years ago (plain frame) were less than $80 delivered to Bangkok.
If you are new to progressives, be aware there will be a perhaps week long acclimation period with distorted perspectives but stick with it and your eyes will quickly self-adjust.