You seem to be using the cost of regulation as an excuse against decriminalisation or legalisation of prostitution which i find wild.
Firstly a slightly higher cost to cover overhead would be fine for most johns if they didn’t have to risk jail I’d imagine. I’m also sceptical that would even be needed. My understanding is currently in the US pimps take the majority of what sex workers earn.
Remember theres also tax revenue generated here so that would easily cover any government oversight…or does in other countries.
Also take into account that cost of not regulating is far far far higher. It’s like the cost of homelessness - it costs massive amounts to a community oddly! The medical, policing, social services etc etc not to mention cost in terms of violence from criminal behaviour, drug addiction etc etc… At the end of the day it bringing people into society is a far better option for all.