Another thought; perhaps infantry could have the worst cost:cost maintenance ratio. for instance, 1% maintenance cost for each sector occupied by an infantry compared to 0.75% cost for a jeep, 0.50% for a tank. or however the maintenance fees currently work. Massing infantry would still be the most cost-effective SHORT-TERM tactic, but allowing a plethora of infantry sitting around doing nothing would make a considerable blow to your daily income, could possibly do something about it.

As mentioned earlier, the problem is that the real cost of infantry is TIME -- the time to go clicking for hours to use as many infantry as possible in order to maximize the efficient use of your available $. I was using tanks because I ran out of time to devote to the game. I fundamentally disagree with games using time-wasted as a significant measure of determining victory.

As Johnny also noted, a UI fix is probably the best way to go.