Is there any sources for it? Or have anyone thought about it?
As far as I can see from wikipedia, prices in ancient Greece ranged from 1/2 - 6 days wages for a skilled labourer, for a Pornai - prostitute who serve multiple customers in a day, and more for a Hetaera - one hired for a longer period of time, exclusive for a single customer. Sounds pretty fair to me.
If I recall correctly, prostitution was priced in 1E D&D. For Dark Sun, I’d say an encounter with a sex worker is as low as 1cp and as high as 1gp, depending on the specific circumstances and venue.
Page 52 of the The Complete Guide to Unlawful Carnal Knowledge offers some useful thoughts on the matter, though perhaps that book was not composed by the most studied pen.
A deeper perusal of historical works might be illuminating. In Balic, I mean Hellas, I am to understand there was quite the price difference between a sophisticated courtesan and a common hooker.
If I ever draft some basic tables on this, I’ll be sure to post.
In Ancient-Greece, the flute-girls that attended dinner-banquets were usually prostitutes, and they attended the upper-class. No prostitute really wants to service the lower-classes, unless they have to.
In a post-apocalypse like Dark Sun, I’d say, they’d also barter for things like, you know, water.