Major ICs NEED to be expensive. I realize they are extremely rarely purchased. One reason for that is the very strict placement limitations – Must be your own original territory and worth 3 IPCs or more.
So, as for the cost of 30 IPCs. There are only 3 nations that could purchase a Major IC with their starting income: USA, Russia and Germany. The USA can’t place any because outside of their three main territories E USA, C USA and W USA, which already have Major ICs (or will as soon as they are at war), no other territories are expensive enough to handle a Major IC. Russia doesn’t have any original territories outside of Russia itself worth 3 or more IPCs.
So, that just leaves Germany with 5 original territories that are capable: Norway, Holland/Belgium, Greater Southern Germany, Hungary/Slovakia and Romania. If we lowered the cost of Major ICs too much, could you imagine Germany with 7 Major ICs? On the other hand, why would they need that many and how much could they really afford to place at them?
The ability to plop down 10 units at once in one place is pretty powerful. If Major ICs were any cheaper, it might make those countries too strong. This would only help out the Axis powers by the way. Besides Germany, the only other countries that would have the capabilities of purchasing a Major IC are Japan (Korea), Italy (S Italy and that would simply be an upgrade) and France (S France, also an upgrade). Although France is an Ally, this would not be a benefit to them no matter how low you made the cost because they usually get taken out Round 1 and even after being liberated are never in any position to purchase an IC.
By the way, the only games I have seen a Major IC purchased was by Germany when they decide to forgo Sealion and head right into Barbarossa. They plop a Major on Romania to build a strong southern army and take the Ukraine, Caucasus and Stalingrad fairly quickly.