If you can read the manuals, self build is the way to go. For example, I just finished a new gaming box for Witcher III. The case was a Lian-Li mid tower for around $100. The processor was an AMD FX8350 (octal core), and the mobo was a Gigabyte 990FX-UD3 which supports up to 32 gigs. That was around $280. Video card is a Geforce 960 GTX at $199. BD burner was $55. 1tb HDD was $60, and the boot drive is a 256gb Samsung vertical stack SSD that was $120. Power supply was one I had on hand, but a good 800watt is around $100.

So around $850 with tax, with plenty of room to expand the storage and Ram (it has 8 gigs DDR3 that came as part of the sale price on the cpu/mobo combo). No muss, no fuss, no customized components or power connectors. All the goodies are ANSI VESA industry standard, which frees you to shop at any hardware vendor for replacement or upgrade components.