Depending on how game you are you could build your own NAS box like I did
All you need is an old PC, doesn't have to high spec
A bunch of HDD's
Some sort of PCI sata controller (if your pc doesn't have enough sata ports)
Freenas- it's a linux based program
http://www.freenas.org/
Basically you install it to a thumb drive and it boots up. I didn't explain it very well but have a look on the website, all very self explanatory. I've got 6 x 500GB HDD's running in a raid 5