I would use:
http://www.superbiiz.comYou can pick whatever parts you want (you can use their "system builder" functionality on their web site to pick from a huge assortment of motherboards, CPU's, RAM, PSU's, graphics cards, cases, etc.), they assemble it, test it, ship it to you, and give you a 1-year warranty on the whole system.
Here's a build for $550, giving an i5-6400 CPU, 8 GB RAM, 1 TB hard disk, 520W PSU, and Windows 10:
Thermaltake V3 Black Edition VL80001W2Z No Power Supply Mid Tower (Black)
GIGABYTE GA-H170-D3HP LGA1151/ Intel H170/ DDR4/ 2-Way CrossFireX/ SATA3&USB3.1/ M.2&SATA Express/ A&GbE/ ATX Intel Core i5-6400 Skylake Processor 2.7GHz 8.0GT/s 6MB LGA 1151 CPU, Retail
2x Samsung DDR4-2133 4GB/512Mx8 CL15 Desktop Memory
Seasonic S12 II Bronze 520W 80Plus Power Supply
Seagate Barracuda ST1000DM003 1TB 7200RPM SATA3/SATA 6.0 GB/s 64MB Hard Drive (3.5 inch)
Microsoft Windows 10 Home Operating System 64-bit English (1-Pack), OEM
Then you can add whatever graphics card you want to the build. Say you pick one in the $150-$200 range, then you have a machine that will do great at AH3 for $700-$750.
Or you could even go to a build with an i3 CPU, a slightly cheaper motherboard, and a 500 GB HD and shave $100 off that.