You honestly don't want to go too cheap on a PSU. SR-71 will say it best.
But why not go with something that doesn't require two connectors, like the GTX 1050 2GB or even the 4GB. That 580 is so outdated it's not even funny. You might can try the 1050 Ti as well. If not go with the RX 560 or 570. That way you can get a PSU that will still perform well. A favorite of mine is the SeaSonic 520w. It's only $50 and goes what it needs to do.
EDIT: looks like I was a bit too late.