Oh, and pricing...not exactly sure. I suggested 5,000 shilling (equivalent to $50) and it got accepted without question every time. To put it in perspective, some of the local girls in Diani Beach have come from Mombasa to cut their travel time. They rent a small room off the beach for 2,000 shilling a month ($20). One told me she came from Nairobi for work and that her rent in Nairobi was "very high" at 5,000 shilling / month.
If you are really tight, you might suggest less, possiblly a lot less. If you are from a western economy and in Diani Beach on vacation paying $50 for an hour is a bargain, and you might consider that the girls need the money more than you do.
Most of the girls I met were in their mid-20's...very beautiful.