I feel like that your CVE should be at least as in heavy cruiser is to battleship in terms of cost. Historically Essex cost 40-80mil with like one of the earlier CVEs costing around 4 mil perhaps. That's not a 30% of a cost of CA>BB, but 10% of the cost. Granted they're slow as ♥♥♥♥, and are a disaster at that, but given that they're hardcoded limits on amount of carriers you could stick into a fleet that mechanics pretty much ensures that you'd mirror the disposition of those times to not try and expect to reign supreme in high seas with CVEs. Although you'd want to watch out for a thing where if you have more than 20 carriers in a fleet the penalty is mitigated completely, with fleet acting as if it has 4 ships. I wouldn't worry to much about this, as generally carriers will first target each other and if you make sure that CVE are explody and etc as they were the 20+ CVE fleet will quickly wind up in very sub-optimal situation of like 5-20 CVEs.

PS with your basic CVE having that capacity of like 20% of the carrier you're then basically looking for 100 CVEs for a doomstack with cost of airplanes aside, that basically comes out at 10 full blown carriers if you really go and make CVE have like 10% the cost and wish to make a doomstack with CVEs of 100+ in a fleet to "rape" the conventional fleet.