To run 3 monitors you'd need a $500 graphics card eg
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121779&cm_re=asus_gtx_780-_-14-121-779-_-Product
There's Tom's $800 -
http://www.tomshardware.com/reviews/build-your-own-budget-gaming-pc,3780.html
or
CPU: AMD FX-6300 3.5GHz 6-Core Processor ($109.99 @ Newegg)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($29.95 @ Amazon)
Motherboard: Asus M5A97 R2.0 ATX AM3+ Motherboard ($88.79 @ Newegg)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory ($77.25 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Amazon)
Video Card: MSI GeForce GTX 760 2GB TWIN FROZR Video Card ($249.99 @ Amazon)
Case: Corsair 200R ATX Mid Tower Case ($57.99 @ Micro Center)
Power Supply: SeaSonic G 550W 80+ Gold Certified Semi-Modular ATX Power Supply ($79.99 @ Amazon)
Total: $743.94
or
CPU: AMD FX-8320 3.5GHz 8-Core Processor ($149.99 @ SuperBiiz)
Motherboard: Asus M5A97 R2.0 ATX AM3+ Motherboard ($94.99 @ Amazon)
Memory: Team Vulcan 8GB (2 x 4GB) DDR3-1600 Memory ($69.98 @ OutletPC)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($58.99 @ NCIX US)
Video Card: PNY GeForce GTX 770 2GB Video Card ($315.68 @ B&H)
Case: NZXT Source 210 (Black) ATX Mid Tower Case ($37.99 @ Microcenter)
Power Supply: Corsair Builder 600W 80+ Bronze Certified ATX Power Supply ($64.70 @ Amazon)
Optical Drive: LG GH24NSB0 DVD/CD Writer ($15.99 @ Microcenter)
Total: $808.31