SetsulBudget shouldn't be a problem so let's focus on performance.
i5 should be enough.
Define decent GPU.
SSD size? HDD?
µATX ok or SLI/Crossfire or lots of PCI(e) cards planned?
CPU i5 GEN 6
Kingston 240GB SSD
Seagate HDD 1TB SATA 3.5 Surveillance
Kingston 8GB 2133MHz DDR4
I think this is quite enough for a gaming computer.