Then I'd say you're probably looking at a 400 watt PSU as a rule of thumb; a 400 to 450 is probably a safe bet. Here's matching PSUs at newegg- there's more details that need to be taken into consideration, like how many 12v connectors and whether you have a 20 or 24 pin main connector, but it's a decent reference for price ranges and narrowing things down a bit.