This is about as cheap as I could go without seriously sacrificing quality.
AMD
PCPartPicker part list:
http://pcpartpicker.com/p/RrjhdC
Price breakdown by merchant: http://pcpartpicker.com/p/RrjhdC/by_merchant/
CPU: AMD A4-6300 3.7GHz Dual-Core Processor ($37.99 @ Newegg)
Motherboard: Asus A78M-A Micro ATX FM2+ Motherboard ($49.99 @ Directron)
Memory: G.Skill Ripjaws Series 4GB (2 x 2GB) DDR3-2000 Memory ($44.99 @ Newegg)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($77.75 @ OutletPC)
Case: Silverstone ML04B HTPC Case ($71.30 @ NCIX US)
Power Supply: Antec EarthWatts Green 380W 80+ Bronze Certified ATX Power Supply ($29.99 @ Newegg)
Wireless Network Adapter: Rosewill RNX-N150UBE 802.11b/g/n USB 2.0 Wi-Fi Adapter ($13.99 @ Amazon)
Total: $326.00
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-12-28 00:21 EST-0500
Intel
PCPartPicker part list:
http://pcpartpicker.com/p/cQW6P6
Price breakdown by merchant: http://pcpartpicker.com/p/cQW6P6/by_merchant/
CPU: Intel Celeron G1840 2.8GHz Dual-Core Processor ($42.98 @ OutletPC)
Motherboard: Asus H81M-D PLUS Micro ATX LGA1150 Motherboard ($44.49 @ Newegg)
Memory: G.Skill Ripjaws Series 4GB (2 x 2GB) DDR3-1600 Memory ($34.99 @ Newegg)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($77.75 @ OutletPC)
Case: Silverstone ML04B HTPC Case ($71.30 @ NCIX US)
Power Supply: Antec EarthWatts Green 380W 80+ Bronze Certified ATX Power Supply ($29.99 @ Newegg)
Wireless Network Adapter: Rosewill RNX-N150UBE 802.11b/g/n USB 2.0 Wi-Fi Adapter ($13.99 @ Amazon)
Total: $315.49
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-12-28 00:23 EST-0500