Here's 3 builds, ordered in what I believe to be incrementally better with each revision, though all valid options...
$650 PileDriver build (good):
CPU: AMD FX-8310 3.4GHz 8-Core Processor (~$115+$5S/H @ Tiger)
CPU Cooler: RAIJINTEK AIDOS 48.6 CFM Sleeve Bearing CPU Cooler ($23.00 @ Amazon)
Motherboard: Gigabyte GA-78LMT-USB3 Micro ATX AM3+ Motherboard ($60.98 @ Newegg)
Memory: Mushkin Stealth 8GB (2 x 4GB) DDR3-1600 Memory ($60.98 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($50.96 @ Directron)
Video Card: MSI GeForce GTX 750 Ti 2GB Video Card ($126.98 @ Newegg)
Case: Cooler Master N200 MicroATX Mid Tower Case ($44.98 @ Newegg)
Power Supply: Rosewill Capstone 450W 80+ Gold Certified ATX Power Supply ($59.99 @ Amazon)
Operating System: Microsoft Windows 8.1 - 64-bit (OEM) (64-bit) ($92.00 @ B&H)
Total: ~$640 TO THE DOOR (includes shipping from merchants selected, no MIRs).
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$650 Haswell build (better):
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i5-4440 3.1GHz Quad-Core Processor ($174.99 @ NCIX US)
Motherboard: Biostar Hi-Fi H81S2 ATX LGA1150 Motherboard ($49.99 @ Amazon)
Memory: Mushkin Stealth 8GB (2 x 4GB) DDR3-1600 Memory ($60.98 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($50.96 @ Directron)
Video Card: Sapphire Radeon R7 260X 2GB Video Card ($122.98 @ Newegg)
Case: Deepcool TESSERACT WH ATX Mid Tower Case ($37.98 @ Newegg)
Power Supply: Rosewill Capstone 450W 80+ Gold Certified ATX Power Supply ($59.99 @ Amazon)
Operating System: Microsoft Windows 8.1 - 64-bit (OEM) (64-bit) ($92.00 @ B&H)
Total: $650 TO THE DOOR (includes shipping from merchants selected, no MIRs).
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SSD + haswell (best):
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i5-4440 3.1GHz Quad-Core Processor ($174.99 @ NCIX US)
Motherboard: Biostar Hi-Fi H81S2 ATX LGA1150 Motherboard ($49.99 @ Amazon)
Memory: Mushkin Stealth 8GB (2 x 4GB) DDR3-1600 Memory ($60.98 @ Newegg)
Storage: Crucial MX100 256GB 2.5" Solid State Drive ($99.99 @ Amazon)
Video Card: PowerColor Radeon R7 250X 1GB Video Card ($79.99 @ Newegg)
Case: Deepcool TESSERACT WH ATX Mid Tower Case ($37.98 @ Newegg)
Power Supply: Rosewill Capstone 450W 80+ Gold Certified ATX Power Supply ($59.99 @ Amazon)
Operating System: Microsoft Windows 8.1 - 64-bit (OEM) (64-bit) ($92.00 @ B&H)
Total: $656 TO THE DOOR (includes shipping from merchants selected, no MIRs).
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There's a lot of misconception about how much GPU is required to play games. In fact, the vast majority of current production GPUs can play any game made without complication, especially at 720P:
http://www.tomshardware.com/reviews/crysis-3-performance-benchmark-gaming,3451-4.html
Notice that at 720P at the low detail preset, the GTX650, HD7750, HD7770 (=R7 250X), and GTX650Ti are all actually bottlenecked by the i7-3960X. The HD7770 is a decent step better than the GTX650, as such, should have no problems with a a slightly higher visual quality setting than was chosen for the test...
Quote
"Crysis 3 gives us more eye candy and a similar combat experience as its predecessor. The highest settings are absolutely brutal on high-end hardware. But there's good news: this game's lowest detail setting looks far better than many other games' highest quality levels, and even a sub-$110 Radeon HD 7750 or GeForce GTX 650 is playable at 1920x1080."
As it would turn out, every game made has settings that will run fine on a $100 GPU.
Check this:
http://www.tomshardware.com/reviews/radeon-r7-250x-graphics-card-review,3747-3.html
250X running seriously demanding games at 1080P getting 30-60FPS range with reasonable visual quality settings. Just a reminder, 720P is half as many pixels for the GPU to deal with as 1080P.