See the link in my sig.
MAKE the budget for a good one. The PSU is the lifeblood of your system. A low quality PSU can provide poor/unsteady power levels, and hurt performance and component longevity, or it can fail, and can take out expensive components with it. It might also be something of a fire-hazard.
A rock-solid PSU is something you MUST have, and one of those things that you NEVER want to have to worry about.