SOme good advice above,
Going 'Cheap' on a PSU is the worst thing you could do.
'Cheap' PSU's don't have some features which protect other compoennts if the unit fails. I have even seen picture of some 'cheap' PSU's on fire.
Its best to stick to a good brand like Seasonic, Antec, Superflower, Be Quiet or even Corsair.