http://www.pcgamer.com/pc-build-guide-budget-gaming-pc/

Building PCs for gaming can get expensive. It’s easy to put together a cart or two that quickly swells to two or three thousand dollars. Can everyone afford such a machine? No. Some—actually, many—people have stricter budgets and bills to pay. But that doesn’t mean you can’t build a PC you can be proud of. If you're prudent about part choices, you can still build an impressive PC that will run today's games great and upgrade well in the future.