Depends on the venue, club and series, but generally the organising club charges the series/drivers money which they use to pay the owner for the hire of their circuit. Gate money can go to either or split between organiser and owner.
A Club - BARC/BRSCC/etc - bids to run a series/meeting, so they have estimated how much it will cost them, and how much profit they can make. Sometimes they get it wrong - and I'm not talking SCSA here.
Obviously the V8's must have done their sums, and believe 2008 will be cheaper by becoming part of another package, which unfortunately for us does not run at the Rock.
At the end of the day everyone is part of the money-jigsaw