I don't think this is something that can really be fixed simply by adjusting costs, build times, etc.
Personally I think air needs to be rebalanced as a whole. T3 is always going to be rushed to simply because the first team with it has such a massive advantage. T2 air snipes will always be an efficiency goldmine because the cost to stop one is way more than the cost to execute one.
The first problem being that you will always need to invest more in static and mobile AA to deter t2/t3 air snipes than the player investing in the snipe will, not including what you'll lose due to said snipes or bombing runs. Whether this is actually a problem or just a fact of life, is up to the balance team. Either static AA needs to be cheaper, or mobile AA needs to be stronger.
Next, not having T2 fighters for all factions is what leads to ASF being to OP in the first place. Inties will simply never stand up to ASF. If players had better options for T2 air-to-air, I don't think we'd see the rush to T3 be so mandatory.
Obviously this isn't a total solution, but I think these two things would go further than adjusting build times and such.