Is there a better build for $800-850?

Solution
You need a Skylake chip to update that B150. B250 works straight out of the box. More RAM. Better GPU.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-7500 3.4GHz Quad-Core Processor ($189.75 @ OutletPC)
Motherboard: Gigabyte GA-B250M-DS3H Micro ATX LGA1151 Motherboard ($68.99 @ SuperBiiz)
Memory: GeIL EVO POTENZA 16GB (2 x 8GB) DDR4-2400 Memory ($94.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($49.33 @ OutletPC)
Video Card: Gigabyte GeForce GTX 1070 8GB Mini ITX OC Video Card ($369.98 @ Amazon)
Case: Thermaltake Versa H21 ATX Mid Tower Case ($36.50 @...
You need a Skylake chip to update that B150. B250 works straight out of the box. More RAM. Better GPU.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-7500 3.4GHz Quad-Core Processor ($189.75 @ OutletPC)
Motherboard: Gigabyte GA-B250M-DS3H Micro ATX LGA1151 Motherboard ($68.99 @ SuperBiiz)
Memory: GeIL EVO POTENZA 16GB (2 x 8GB) DDR4-2400 Memory ($94.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($49.33 @ OutletPC)
Video Card: Gigabyte GeForce GTX 1070 8GB Mini ITX OC Video Card ($369.98 @ Amazon)
Case: Thermaltake Versa H21 ATX Mid Tower Case ($36.50 @ Amazon)
Power Supply: Corsair CXM 450W 80+ Bronze Certified Semi-Modular ATX Power Supply ($33.98 @ Newegg)
Total: $843.52
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-23 20:13 EDT-0400
 
Solution

logainofhades

Titan
Moderator
With it being the single fan 1070, 450w is actually ok, for that rig, imo. A little headroom doesn't hurt, though.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-7500 3.4GHz Quad-Core Processor ($189.75 @ OutletPC)
Motherboard: ASRock B250M Pro4 Micro ATX LGA1151 Motherboard ($77.98 @ Newegg)
Memory: PNY Anarchy 16GB (2 x 8GB) DDR4-2400 Memory ($89.99 @ Amazon)
Storage: Toshiba 1TB 3.5" 7200RPM Internal Hard Drive ($47.89 @ OutletPC)
Video Card: Gigabyte GeForce GTX 1070 8GB Mini ITX OC Video Card ($369.98 @ Amazon)
Case: Rosewill FBM-01 MicroATX Mini Tower Case ($19.35 @ Amazon)
Power Supply: Corsair CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply ($59.99 @ Amazon)
Total: $854.93
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-24 14:52 EDT-0400