Just some options I came up with:
1:
PCPartPicker part list:
http://pcpartpicker.com/p/1WB5o
Price breakdown by merchant: http://pcpartpicker.com/p/1WB5o/by_merchant/
Benchmarks: http://pcpartpicker.com/p/1WB5o/benchmarks/
CPU: AMD FX-8320 3.5GHz 8-Core Processor ($158.98 @ SuperBiiz)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($29.99 @ Microcenter)
Motherboard: ASRock 990FX Extreme3 ATX AM3+/AM3 Motherboard ($104.99 @ Newegg)
Memory: Crucial Ballistix 8GB (2 x 4GB) DDR3-1600 Memory ($69.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($59.99 @ NCIX US)
Video Card: Gigabyte Radeon HD 7970 3GB Video Card ($303.98 @ Newegg)
Case: Antec Three Hundred Two ATX Mid Tower Case ($44.99 @ NCIX US)
Power Supply: Corsair Builder 500W 80 PLUS Bronze Certified ATX12V Power Supply ($24.99 @ Newegg)
Optical Drive: LG GH24NS95 DVD/CD Writer ($15.99 @ Microcenter)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($84.99 @ NCIX US)
Total: $898.88
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-11-02 22:24 EDT-0400)
2:
PCPartPicker part list:
http://pcpartpicker.com/p/1WBeE
Price breakdown by merchant: http://pcpartpicker.com/p/1WBeE/by_merchant/
Benchmarks: http://pcpartpicker.com/p/1WBeE/benchmarks/
CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($219.99 @ Amazon)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($29.99 @ Microcenter)
Motherboard: ASRock Z87 Pro3 ATX LGA1150 Motherboard ($99.99 @ Microcenter)
Memory: Crucial Ballistix 8GB (2 x 4GB) DDR3-1600 Memory ($69.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($59.99 @ NCIX US)
Video Card: Gigabyte Radeon HD 7970 3GB Video Card ($303.98 @ Newegg)
Case: Antec Three Hundred Two ATX Mid Tower Case ($44.99 @ NCIX US)
Power Supply: Corsair CX 750W 80 PLUS Bronze Certified ATX12V Power Supply ($59.99 @ Newegg)
Optical Drive: LG GH24NS95 DVD/CD Writer ($15.99 @ Microcenter)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($84.99 @ NCIX US)
Total: $989.89
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-11-02 22:30 EDT-0400)
These are high-end builds and you probably don't need anything near this cost. (Completely overkill for sims lol).
Do you need a monitor/mouse/keyboard/speakers included with it?