For research purpose where is this?
Pattaya, a coastal city in Thailand where you can get the best
bang for your dollar (if you're into that). It's much safer and low key than places in Colombia or Brazil, but the quality and quantity of cheap young girls supposedly rivals those spots (I've never been to South America though). Pattaya is often viewed as one of the best spots in the world for pay-for-play. Again, due to the abundance of young, fit, asian girls who are willing to do a lot for relatively little.
You'll find a bunch of young Thai girls from smaller cities who travel anywhere from 2-10 hours to setup shop in Pattaya. It's basically a hot spot for Eurotrash dudes, and increasingly for Asian and Indian guys looking for a good time and cheap p*ssy. There's also a fair amount of families who are looking for a cheap coastal vacation.
There's also a bunch of Russian girls and clubs, but they tend to be more expensive.
For girls, Bangkok, especially around Nana Plaza, probably has higher quality girls and more international flavor. There are girls from all over S.E. Asia (Cambodia, Vietnam, etc.), a bunch of African chicks, Russian girls, etc. But prices tend to be higher and the girls are more likely to scam or want something for nothing.