You shouldn't cheap out on the power supply, but the bronze, silver, & gold ratings are less important than the quality. They just tell you how efficient the PSU is so the better the rating the less it will cost you to run the PC, but we are probably talking about a few cents a week at the most unless your power is really expensive.
I would google a review for any PSU you are considering and at least read the conclusion, or post the models here for an opinion.
The PSU has the power(pun intended) to destroy the whle computer so it should be one of the better components.