So if a girl asks for over $100 you act surprised and have a pocket with $103 take it out and start to count. "Sorry I only have $103 and I need $3 to get back home, I'll just have the massage today, no extras" Then say "Coco or Tina or Asia, make up a name, at the Spa down the street only charges $100"
I guarantee she will accept that price and she will continue to charge you $100 on future visits.