R7 260X is a faster GPU even in gaming, and in mining AMD is way ahead still.
You should get a cheap mobo with many PCI ports (for multiple GPU's), the CPU should also be extremely cheap, most people probably use a single-core CPU here.
You should also overclock the GPU to it's max potential, try hitting max 80-85 C with 70-85% fanspeed, and get the highest possible overclock. With this card you might not hit the max C, so you could relax the fanspeed a bit to take some stress from the fans.
Should also be worth getting a XFX Proseries XXX edition 550w, will stay around ~50% load, which is the PSU sweet spot for efficiency, since you're going to have this running for quite some time for mining, it's not bad to not use a couple of percent less wattage, and the XFX is cheap too.
Basically a mining rig is using as little on anything not named GPU, and max possible budget on GPU's.
Im not a master nor pro at btc mining, but i have some understanding about it, which i threw at you in this post.