Oh, by the way, smaller air groups are far more plausible too since that’s where so much of the expense will be.
An RAN with two Invincibles in the mid ‘80s would obviously need a larger Fleet Air Arm than historically, but what would be a reasonably affordable inventory?
A modest standard air group might be four Sea Harriers and six Sea Kings - one or two of the latter being AEW variants.
You might work on the assumption that the RAN should be able to have available sufficient aircraft of each type for two such air groups and then enough for a third to effectively augment one of the air groups if needed.
Thus, working on the ratio I’ve heard of 3-1-1-1 for fighters (i.e. for every 3 a/c ready for operations, you need one in squadron maintenance, one in deep maintenance / attrition, and one for pilot conversion), you’d need at least 24 Sea Harriers, 20 single-seater and 4 two-seaters. But you might have a couple more of each.
Helicopters are a little different, but let’s say 30 Sea Kings, including 6-8 AEW variants, and probably across two squadrons rather than one.
So, yeah, even for the small Invincibles with modest air groups we’re looking at 50-plus more aircraft than were in service historically.
And then in the future you’re going to have to replace all of those aircraft before the ships themselves are due for the scrappers.
Though, on the fighter front, Australia could save a dollar or two in buying ex-British Harrier IIs.