I bought mine many years ago at a stall in a Pattaya market. I think I paid 100 baht a pair about.
Rated for reading :125 and 150. I tried 175 but it's too much for me.
Before moving back to BKK and then Ubon I bought a few (many!) pairs.
Eventually, they do get scratched and I throw them away.
I've looked at Lazada and, indeed, I would buy cheap there if I need new ones.
I have no need for an expensive oculist shop and for "prescription" glasses even though I'm a very senior guy...😀