What country? If US, what City/State? [Because if you are near a Microcenter or Fry's Electronics, their in store specials are sometimes better than online. Also, sales tax issues.]
Also, check out youtube for many instructional videos on PC assembly.
Offhand, I think your budget is in the territory of a [i5 3570k, HD 7870 2GB, 7870 XT or GTX 660 Ti & 8GB RAM ...depending on what we can do to shoehorn the remaining necessities. Don't forget the OS will run ~$100 on its own.]