What I would probably do is upgrade the gpu first with a 760. And later on, when you have some more cash upgrade the cpu/mobo (im assuming you have DDR3 Ram)
But than you could go for something like this
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($199.99 @ Microcenter)
Motherboard: ASRock Z87 Extreme3 ATX LGA1150 Motherboard ($127.99 @ Newegg)
Video Card: MSI GeForce GTX 760 2GB Video Card ($255.66 @ Newegg)
Total: $583.64
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-07-03 03:51 EDT-0400)
If you want it all, you could get this:
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($199.99 @ Microcenter)
Motherboard: ASRock Z87 Extreme3 ATX LGA1150 Motherboard ($127.99 @ Newegg)
Video Card: Gigabyte GeForce GTX 650 Ti Boost 2GB Video Card ($172.98 @ SuperBiiz)
Total: $500.96
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-07-03 03:52 EDT-0400)
And if you dont want to OC, you can get this:
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
CPU: Intel Core i5-4570 3.2GHz Quad-Core Processor ($159.99 @ Microcenter)
Motherboard: MSI B85M-G43 Micro ATX LGA1150 Motherboard ($79.99 @ Amazon)
Video Card: MSI GeForce GTX 760 2GB Video Card ($255.66 @ Newegg)
Total: $495.64
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-07-03 04:15 EDT-0400)
If that is to much, you could drop the GPU down to a 660. But you will quite some performance in the GPU deparment.