You know, I keep running into folks who say that, yet can't prove it with the math.
Show me a NAS box that beats $2/25GB storage. Even without any RAID, or with minimal, at any price/storage size. So, show me what box, at what size, you're talking about, that beats that figure. This without bringing up the fact (with burnable discs) that it's an unlimited (and flexible) storage medium.
At $2/25GB, that would equal 40ea for 1TB, and so a 1TB disc would have to be $80 (or double that for a 2TB disc), and without a case, plus if a RAID array, without the h/w supporting that (and I'm not figuring that it'll actually be smaller due to formatting) plus of course more disc space needed for the type of RAID wanted.
Even if one ramps up the sizing to get the maximum price ratio, it doesn't work out. I know, as I have a 18TB Raid array. It's good for 'temporary' storage, but not for very long term.