I would buy a Corsair CX550 80+ bronze. $49.99 directly from Corsair.
The cx450 and Cx550 offer good quality, quiet operation, and enough wattage for a 570.
the s12ii series that ends with 50 or 00 are not made by seasonic and are junk.Dang, turkeys not on pc part picker.
Really, i wouldnt go much cheaper than the CX grey lineup of power supplies.
The seasonic S12 450w 80+ bronze is about $40 and will reliably power an rx570, however the S12 platforn is nearly a decade old.