A good start would be to pick up a new i6 6100 for example paired with a 950-960 or a 370, standard 8GB ddr4 2133mhz ram module(or kit 2*4), a nice enough case while not going for things you don't need in it(just a plain atx case or if you want smaller an htpc/itx chassis that fits the stuff you would like to put into it), a 450-550 watt power supply(for example a corsair cx450 should do just fine) and a complementary z170 motherboard in the correct size(itx/atx).
It will perform nice enough to play games like GTA 5 at high settings and if you go for the amd 370 card you usually get 4GB vram, this could help in the future to get more games to higher settings while not affecting framerate alot(if it goes over the 2GB vram usage).
I'm actually going to be building a very similar build for a friend and so far i haven't come across better value for money than this.
Hope this helped you a bit and good luck.