If you want to use this purely as a NAS, buy a NAS simply because it will use less electricity. If you want storage and have the ability to do other things, buy a used server. DL370's, R410's, R210's are all getting insanely cheap these days. All can be had with at least 16gb of ram and sometimes RAID controllers for under $100.
Of all the branches of men in the forces, there is none which shows more devotion and faces grimmer perils than the Submariners." - Sir Winston Churchill.