It makes sense that if it were legalized in other states, like gambling, that the price would go down. But I haven't noticed that as far as casinos go. [Perhaps it could be promoted because the taxes, after all, would go to help fund education, like lottery money does]. If, after a while, the customer base dropped off, the prices would logically fall, too. I don't imagine I'd be around long enough to see that happen.
I can see pimps getting involved and getting a cut (and as a result, inflating prices) and once government gets their hooks in, they would also inflate prices. On the other hand, if it were legal every place, larger cities would definitely have the finer women and higher prices, the smaller towns and rural locations, the less attractive ladies and probably cheaper prices. Doubtless, it would spell doom and gloom for some of the rural Nevada houses we have all grown to know and love.
And overriding all of this, any time government gets involved in business, the unlikeliest of spin-offs will occur. Can you imagine the public backlash that will occur when a slew of young, just-out-of-high-school girls decide to get in the business? Or when some not-quite-out-of-high-school girls decide that it would be a good way to earn money (better than a car wash or bake sale) [think "Risky Business"]? Or a bored house wife (I assume that they still exist) takes up the hobby to supplement the household income -- what happens if the husband finds out or protests? Fun points for conjecture.