Its just the marketplace rules really. Some of the best sex I've ever had was in Thailand, and no, not in the normal 'mongering' type scenario at all, but pricing was under $200 a day. Locally, girls I've gotten to know well tell me their target earn is anywhere from 1000 to 2000 a day, if you're working for a house which takes 40-50% of the client fee then this will dictate to a large degree what you need to charge to reach the target. ie, if you want to earn 1000 a day and the house retains 50% of the fee and you'd like to restrict bookings to say 10 over a 12 hour period then its simple maths, 2000 / 2 (50% house cut) = 1000 / 10 (customers) = 200$ an hour booking fee to the customer. If you only want to see 5 customers day then its $400/hr customer fee.
There is definitely as fine balance going on. Charge too much and the client calls will simply stop, charge too little and you'll certainly be inundated with enquiries but will have to service 10-15 or more clients in a day depending on your target earn. I've seen a couple of private girls start at $160-170, quickly increase that to 250 through 300/hr but then drop back again as clients are very price sensitive. As you approach $300/hr and presuming a fairly attractive WL, the calls will continue to come in, but the clients will start asking for 15 or 20 minute bookings.
Depending on the girl this can be a good or bad thing for them. WL's that I've known will rarely want to have sex or give oral for more than a few minutes, certainly most are not keen on literally bonking for 60 minutes straight, other things come into play, a bit of touch and tickle, perhaps a massage, etc, etc, meaning that for some ladies the 60 minute sessions are preferable to 3x 20 minute encounters where a lot more stress is placed on their bodies in the same period of time.
Everything about this business is expensive. For the private girls you have costs ranging from maintaining a working apartment through to advertising, maintaining a few phones, consumables (condoms/etc), clothing, makeup, possibly hiring a receptionist/phone girl (just not possible to work 10 clients a day _and_ keep comms going), etc, etc, its surprising how this all adds up. Agency girls don't have to worry about the details but will generally lose 40-50% of the direct client charge.