Really it's down to personal choice, both theirs, and the client who sees them (or not...) No one is forcing a client to pay that kind of money, if they choose to purchase that product, that is the price, and it's up to them to either buy, or to pick a different girl's product at a lower price...
Market forces and all that. Anyone in any self employed business can charge whatever they like, just as the client can choose whether or not they pay it...
these girls may be looking to cut down on the number of bookings they get, etc.
Everything balances itself... If they can make the money they want at that price, thats up to them... Maybe they'll find they're not as busy as they want, and drop the fee, or maybe they'll find they wish to further reduce their clients or appeal to a different demographic by upping the fee more!