As Jack says, "Cheap and reliable are kinda mutually exclusive. " While there is some expensive junk out there, you generally do get what you pay for.
My first recommendation for a 500 - 550 watt PSU is this;
I don't particularly care for OCZ because they tend toward incomplete specifications and data plates. For example, what is the maximum 12 volt output current?
And their specs indicate the Zebronics PSU's are junk.