What is netgear rn 31400

http://www.netgear.com/business/products/storage/readynas/RN31400.aspx#tab-techspecs

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.