You wont find an s4 with that budget, but there is a lot of S3's for sale asking around 100$ shipped.  Then just find a good deal on a used PSU,  although i recommend trying to find a good deal on a EVGA 1300W G2,  i picked one up off of ebay for 110 shipped last week..  they are gold rated, and can run 2x S5's or 3x S3's