700$ build with gtx 780?

well a GTX 780 won't leave any room for the other components.
But i have built a rig with the Radeon R9 290 that will give you a great gaming experience:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($174.89 @ OutletPC)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.99 @ Newegg)
Motherboard: Asus H97-PLUS ATX LGA1150 Motherboard ($99.99 @ SuperBiiz)
Memory: Mushkin ECO2 8GB (1 x 8GB) DDR3-1600 Memory ($35.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($45.89 @ OutletPC)
Video Card: Sapphire Radeon R9 290 4GB Video Card ($242.98 @ Newegg)
Case: Enermax OSTROG ATX Mid Tower Case ($39.99 @ Directron)
Power Supply: EVGA 600B 600W 80+ Bronze Certified ATX Power Supply ($39.00 @ Newegg)
Total: $703.72
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-10-18 09:36 EDT-0400


Or you can reuse othe components and buy a GTX 980! (if you have other RAM sticks and the are compatibe - use them)

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($174.89 @ OutletPC)
Motherboard: ASRock H97 PERFORMANCE ATX LGA1150 Motherboard ($79.99 @ Newegg)
Memory: Mushkin ECO2 8GB (1 x 8GB) DDR3-1600 Memory ($35.99 @ Newegg)
Video Card: Asus GeForce GTX 980 4GB STRIX Video Card ($479.99 @ SuperBiiz)
Total: $770.86
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-10-18 09:46 EDT-0400

Have fun!