(Even?) today there are many people involved in the sex industry voluntarily - I know of a Doctor who has left her specialist job to pursue full time sex work, she says it pays more. It’s not so hard to believe that some women 2,000 years ago would have made a good living in a society where this kind of work was accepted and legal.

Presumably a portion could have been previously slaves who earned their freedom; and maybe even some who chose it as a line of work as free women initially