That build is way over your budget. Are you asking to take your build and trim the parts down until we get below $840? If that's what you're asking, here's my best attempt:
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Core i3-4160 3.6GHz Dual-Core Processor | $110.99 @ SuperBiiz |
| Motherboard | ASRock H81M-DGS R2.0 Micro ATX LGA1150 Motherboard | $47.99 @ SuperBiiz |
| Memory | G.Skill NS Series 8GB (2 x 4GB) DDR3-1600 Memory | $66.98 @ Newegg |
| Storage | Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive | $53.97 @ OutletPC |
| Video Card | XFX Radeon R9 290 4GB Double Dissipation Video Card | $264.99 @ NCIX US |
| Case | NZXT Source 210 (Black) ATX Mid Tower Case | $29.98 @ OutletPC |
| Power Supply | Corsair Builder 600W 80+ Bronze Certified ATX Power Supply | $38.50 @ Newegg |
| Monitor | Acer H226HQLbid 60Hz 21.5" Monitor | $119.99 @ Newegg |
| Wireless Network Adapter | Asus PCE-N15 802.11b/g/n PCI-Express x1 Wi-Fi Adapter | $24.99 @ Micro Center |
| Keyboard | Cooler Master Storm QuickFire Rapid Wired Gaming Keyboard | $73.08 @ NCIX US |
| Total | ||
| Prices include shipping, taxes, and discounts when available | $831.46 | |
| Generated by PCPartPicker 2015-01-09 20:07 EST-0500 |