http://pcpartpicker.com/p/2mh2m

CPU: AMD Athlon II X4 750K 3.4GHz Quad-Core Processor ($80.98 @ Newegg)
Motherboard: MSI FM2-A75MA-P33 Micro ATX FM2 Motherboard ($54.99 @ Microcenter)
Memory: Corsair Vengeance LP 8GB (1 x 8GB) DDR3-1600 Memory ($84.79 @ OutletPC)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($59.98 @ OutletPC)
Video Card: MSI Radeon R7 260X 2GB Video Card ($131.98 @ SuperBiiz)
Case: Corsair 200R ATX Mid Tower Case ($49.99 @ Newegg)
Power Supply: Corsair CX 430W 80+ Bronze Certified Semi-Modular ATX Power Supply ($29.99 @ Newegg)
Total: $492.70

Maybe something like this? I'm not too good with US prices though, but that will be able to max out TF2 easily, and will let you run many other games at good settings. I believe it also comes with a free game. :)