Today, my 11 year old joins the PCMR, for $260 I got an Alienware X51 R2 i7-4790K/16GB DDR3/GTX 960, I added an HDD then Win10, pleased to see that his games run
Alienware X51 Processor Installation Guide/ How To Upgrade Alienware X51 CPU Demonstration - YouTube
Alienware X51 R2/R3 CPU Replacement - iFixit Repair Guide