Elizabeth Pisani's post (thanks to MR pointer):
"So a Russian girl is worth twice as much as a girl from north China, huh? And Malaysian girls are discounted fairly heavily. ... If nothing else, I’m happy to note from the poster that all nationalities are working in air-conditioned rooms."
This post switched my preference on Pisani's Wisdom of Whores from maybe to must read even though the answer to this "price puzzle" is not in the book.