I have had a complete reversal of opinion on this topic. The actual additional resources required to provide a three-ship/two-airwing CVA fleet should have been both achievable and manageable within the context of the time. To take things in turn:
Air-wing: Between the RN Sea Harrier force and the Buccaneer and Phantom units assigned to SACEUR for TASMO (Tactical Air Support to Maritime Operations) as a direct replacement for the air wings previously assigned to the RN heavy carriers the aircraft, crews, maintainers etc all existed in reality. The ASW component of those air wings would have been the same Sea King Squadrons that operated from the Invincibles in reality. AEW is less certain but far from intractable, for instance helicopter AEW was studied in the UK in the mid-1960s and I'm sure given an incentive industry would have been happy to extract more life from the Gannet.
Capital Cost: Escorts were built anyway, the RN escort force would not necessarily have had to have been radically different, especially if we assume that the CVA programme is retained whilst the EoS mission is dropped. Money, not as much as CVA01 would have required (thanks
@NOMISYRRUC for your analysis above), was spent building the three Invincible class ships anyway, the escort cruiser would have to be a sacrifice. The actual capital cost of buying the ships, when amortised even over a 15 year period, would likely not have required an unreasonable spending increase compared to what happened historically.
Personnel: CVA01 war complement was approximately 3,000 whilst that for the Invincible's was approximately 1,000. At most, for crew, an uplift of 6,000 personnel would be required over the historical number. Vote A in 1988 was 69,100 so the total Vote A uplift would be less than 10% on even the 1988 number, which itself was much reduced from the 1970s. A good portion of those would have come from a reduced size RAF (approximately four fast jet squadrons less based on that service not providing the TASMO mission, due to the retention of the carriers). Retention and recruitment would have been easier as well, CVA01 was a spacious, fully air conditioned ship designed to the latest habitability standards rather than a modernised WW2 design and inspiring people to join an FAA with a future rather than an execution date should have been a happier experience.
Considered in the round, rather than in isolation, it feels as if a massive loss in national military capability was endured in order to save very little resource in relative terms.