If you decreased the price of ig spawners, you'd need to change everything so the economy stays the same. Iron golems are the best way to make income, and I believe they are fairly priced for what they do. Building supporting grinders, like a cactus farm is also very cost effective. Changing one thing that big could throw the whole balance off. Work your way up to them, so that when you go to buy them, it's a gain not a loss because you have other forms of income.