If you looked at the front page of TomsHardware.com, at the top it says Built it Self systems, if you clicked it and scrolled through the best you can get "low price" for a gaming system HARDWARE is $500 without a keyboard, mouse and monitor (another couple hundred dollars). That still gives no Windows (only W8 is sold in stores) which is another $200, nor any games (depending on the game new ones are $70).
The BEST suggestion would be to just get a off the shelf one at Walmart for $300, that has all the basics and Windows in one purchase. Then save/upgrade the Power Supply (PSUs for $150+) and then the video card ($100+) to get a basic gaming rig.