If your goal is to make 1BTC a week minimum, that would require 2500+ mH/s. With that set up, you will make .06-.08BTC per week. But you have room to add more video cards. Consider an ASIC Miner maybe?
ASICs are expensive and he said he's trying to go cheap. If you want to wait for a while I know of one DIY ASIC project. It's in the planning stages still but it seems to be coming along nicely. I don't have the link at the moment but I'll post it later. Low cost you probably won't get an asic outside of that. There's also 28nm FPGAs coming. I've only seen one but they quoted a 200-300 price range if I remember properly. But that might be a few months off as well.