Not sure if we can fit a monitor on that budget...But if you want suggestion for the rest:
PCPartPicker part list:
https://pcpartpicker.com/list/NcqWd6
Price breakdown by merchant: https://pcpartpicker.com/list/NcqWd6/by_merchant/
CPU: Intel - Pentium G4560 3.5GHz Dual-Core Processor ($59.48 @ OutletPC)
Motherboard: ASRock - B150M-DVS R2.0 Micro ATX LGA1151 Motherboard ($54.99 @ Newegg)
Memory: Corsair - 8GB (1 x 8GB) DDR4-2133 Memory ($61.99 @ Amazon)
Video Card: Sapphire - Radeon RX 550 2GB PULSE Video Card ($84.99 @ SuperBiiz)
Case: BitFenix - Nova ATX Mid Tower Case ($24.99 @ NCIX US)
Power Supply: Corsair - CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply ($39.99 @ Newegg)
Total: $326.43
Prices include...