I've been averaging about $19 per 4tb SAS drive on ebay (refurbs), though sata tends to cost a little more being the more common format. I've had great luck wi

I've been averaging about $19 per 4tb SAS drive on ebay (refurbs), though sata tends to cost a little more being the more common format. I've had great luck with surplus HGST drives, they tend to be more reliable than Seagate.