ORAC and PN -
Exactly. The cost of building the ships is a very small fraction of the acquisition cost of the ships, aircraft and associated equipment, and an even smaller fraction of the costs of operating them - even if all the fancy automation works, the carriers will have a vastly bigger crew than any other surface ship.
I suspect that the current calculus shows that the only way to afford the carriers in the long term is to use the carrier-based aircraft to replace part of the FJ force - which is already up for drastic reductions anyway.
If I had to guess what was being discussed, I would estimate that if the carriers are retained, the RAF/RN will get 75 Dave Bs and (if they are lucky) 100 Typhoons.