I remember one very popular girl (now retired) telling me she'd managed to save £28k in about 6 months. That's save, rather than earn.
And another girl, who said she'd inherited property, and then sold it on for a very large sum - we're talking nearly 7 figures. As to why she was then even bothering to escort, perhaps it's so she could leave the nest egg untouched to accumulate interest?
But I don't think there should be any doubt that the more popular, professional girls are earning some serious poke (if you'll forgive the pun), and can earn it for a long time if they want to stay in the business and look after themselves.