Street price varies of course, so check that on line. At this moment, Amazon US sells it for $613.76. You can buy it with disks installed - generally I've found it is cheaper to buy diskless, and get the disks myself.
There is a hardware compatibility list for drives, google for that and pick drives on the list. I recommend NAS purposed drives - WDC Red, WDC Red Pro, Seagate VN, or perhaps an HGST NAS drive. I use WDC Reds myself.
