All of these girls worked at agencies first started at $250-$300 range. Over the years they become indy and rates keep going up.
I think, most of high priced girls doing this part time bases and kind of side hustle. If they see couple of clients during a week, it is $1.5-$2k for 3-4 hours of total time spent a week or $6-$8k a month. Less work - enough money to live on. For them, this may make a lots of sense.