CS GO - Pentium, 4gb ram and gt730 would do. eg
CPU: Intel Pentium G3258 3.2GHz Dual-Core Processor ($64.99 @ SuperBiiz)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($28.98 @ NCIX US)
Motherboard: ASRock Z97 Anniversary ATX LGA1150 Motherboard ($82.98 @ Newegg)
Memory: G.Skill Ares Series 8GB (2 x 4GB) DDR3-1866 Memory ($67.78 @ OutletPC)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ SuperBiiz)
Video Card: Gigabyte Radeon R7 260X 2GB WINDFORCE Video Card ($112.98 @ Newegg)
Case: Corsair Graphite Series 230T Black ATX Mid Tower Case ($59.99 @ NCIX US)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($44.99 @ NCIX US)
Total: $512.68
plus an OS - total ~ $600