A few things to add in here. Some of these light fleet carriers were picked up used, this is the case for both of Argentina's ships and Brazil's as well. This will affect the acquisition price, although the cost of major upgrades is still very hefty.
Another major cost will be the air wing, these light fleet carriers can only operate a handful of types: Sea Hawk, Sea Venom, Banshee, A4 Skyhawk and Harrier. Replacing these air wings puts a major cost and therefore decision point in front of the Governments involved. Such decisions points aren't just about cost, but also force structure and defence policy in general.
Manning can be difficult for these medium navies. even if they have the cash. The RAN rejected the offer of the Hermes in 1968 because the RAN wouldn't have been able to man it (or at least not easily).
Finally there's a big difference between what a government 'can' afford and what it 'wants to' afford. Below is a chart from
UK Public spending. It shows that while defence spending doubled (1.8b-3.5b) between 1956 and 1972, the years Britain couldn't afford all sorts of important strategic capabilities, it also shows that public spending on the rest of government quadrupled (5.6b - 22.9b). To break this down further, new acquisition is between 25-40% of the force's budget, more for the Navy and Air Forces and less for the Army. It's hard to believe that when a few extra tens of millions would have seen the CVA01 enter service that the government couldn't have found it in the 30b they spent elsewhere in 1967 and 1968.
