You are just a touch over $300 with this build and there is not much you can do short of buying used components to make it much cheaper.
PCPartPicker part list:
https://pcpartpicker.com/list/k2yTXH
Price breakdown by merchant: https://pcpartpicker.com/list/k2yTXH/by_merchant/
CPU: Intel - Pentium G4560 3.5GHz Dual-Core Processor ($82.88 @ OutletPC)
Motherboard: Gigabyte - GA-B250M-DS3H Micro ATX LGA1151 Motherboard ($39.98 @ Newegg)
Memory: Crucial - 8GB (2 x 4GB) DDR4-2400 Memory ($87.99 @ SuperBiiz)
Storage: Toshiba - P300 1TB 3.5" 7200RPM Internal Hard Drive ($39.88 @ Other World Computing)
Case: Thermaltake - Versa H21 Window ATX Mid Tower Case ($19.99 @ Newegg)
Power Supply: SeaSonic - S12II 520W 80+ Bronze Certified ATX Power Supply ($37.99 @ SuperBiiz)
Total: $308.71
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-12-06 14:57 EST-0500