I've never come across someone who charges 150 for an hour and then 50 for the next hour and 30 for the third hour. That is a pretty steep drop.
I've recently put up some reverse bookings for a 2 hour session, and some of the girls that come back to me heavily discount their usual rate!
For £2.00 you can't go wrong. Put one up on AW and watch the bids roll in.