Well newegg has a 4 decent nice combo deals that only need a OS.
I am pretty sure the family you are building it for can get a student price on a OEM copt of window7 64bit or 8.1 whatever is cheaper.
There are 2 haswell systems with I5-4430 3.0ghz systems bit with only 4GB of ram one has a ASUS motherboard with aAsus gtx 650ti NON BOOST for $588.49 http://www.newegg.com/Product/ComboBund ... bo.1413489
The other Haswell system also has the I5-4430 CPU with a EVGA 650ti NON BOOST for $545.49http://www.newegg.com/Product/ComboBund ... bo.1430436
All the systems come with a single stick of memory. It will cost $36 to get another stick of drr3 1600 for the haswell systems so dual channel memory works.
The other 2 systems have single 8gb sticks. The AMD system will cost 75.99 to add another 8 gb stick of 1866 gskill memory. The ivy Bridge system will cost $78 bucks for another stick of 8gb gskill memory.
One is AMD FX-8350 based with a MSI HD7850 2gb for $610.99 but has no CD drive. http://www.newegg.com/Product/ComboBund ... bo.1492556
Another system is a Ivy bridge Intel I5-3350p 3.1-3.3ghz CPU and a MSI 1gb gtx 650ti boost card. this system comes with a cd-drive. I think this system has a nicer case with 3 120mm spinners. front, rear and top. But the top one can be put in the side panel as a intake that is a much better configuration then a top exhaust fan plus it helps cool the GPU and CPU along with the motherboard chipset and VRMs. $608.49 http://www.newegg.com/Product/ComboBund ... bo.1453605
I think I would definitely go with the cheaper Haswell based machines at the top Plus it will only cost $36 to enable dual channel memory and a total of 8gb of memory is fine. 16gb is a little overkill more so when it will cost 76$ + just to get dual channel working. but I think the Intel systems will run better on a single channel then the AMD system.
But the best performing system for gaming "as is"would be the last one I listed. The Ivy bridge with the 650ti boost card that is much faster then a regular non boost 650 card. Too bad they do not have the IVY system paired with the MSI hd 7850 2gb card.
2600k@4660mhz CM Nepton40XL 16gb Ram 2x EVGA GTX770 4gb Classified cards in SLI@1280mhz Stock boost on a GAP67-UD4-B3, SBlaster Z powered by TX-850 PSU 2xHTPC's Both w/i3 2120's,1xasus LP HD6570@850core 1000 ddr3mem 1xHIS hd7750@1125core1400mem