Well, you'd need to buy hard drives anyway with an off the shelf NAS, if you can throw a PC together for cheap it's not like a major investment to try this route, and if you want to get a QNAP or whatever later, you just reuse the drives. FreeNAS and OpenMediaVault are popular options.
Edit: I just realised that you started this thread in 2014 and still haven't bought NAS yet