I don't think that the price for heroes is too damn high, but you should be able to earn more money faster. Like, you need friking 80 victories to get a hero, a mission well done should give like at least 200-250 money und there should be more ways to get it, achievements, goals, side-quests, challenges, campaign etc.. The game is awesome, apart from that.
Nice idea. I'm thinking about that, but likely this will be implemented in sequel.