I don't know if anyone has already mentioned this, but don't cheap out on the motherboard. You're better off paying an additional $50 with up to four slots for RAM and more PCI e slots. You might want to upgrade RAM and you might want to add a capture card in the future. Having a cheap motherboard you're really just limiting yourself and not giving yourself any room to upgrade.
Also, with Windows 7, that's another $90, so with a decent montherboard you'll looking looking at $700. It's more powerful than the PS4, but it will probably run the games just as good as the PS4. So what's the point in paying almost double for multiconsole games that are going to play the same.
If you build a PC that weak you might as well use it for exclusive games unless you're not interested in getting consoless at all.
