The QE's were supposed to be designed so they could eventually choose Cats & traps. But as ever the politicians were happy with the "promise" and never nailed down the costs
Surprise, surprise, when BAe etc were asked later for an estimate it was vast and on a programme that was already eating cash and resources it wasn't affordable at the time.
Long term cost was that the RN is stuck with the B variant for all time. The RAF has the option of buying A or C versions going forward.