Interesting, have only used agencies a couple of times, usually use independents via phonebox cards in the old days , PN, A work, their own sites and so on.
Abt 12 yrs back saw 1 lady in Sth Ken area via an agency couple of times, £200 ph but top notch punt/smart location/no rush
After my 3rd visit she gave me her direct number, reduced to £160 ph so pres she was giving away more than £40 to agency?
Suited me as saved my time and money for direct booking, became a regular for a while until like they all do she disappeared into the sunset!
Not used an agency since so don't know if such "offers" are still available? - subject to research I guess!