See, I'd disagree with TB (when does that ever happen?
)
I have two (rather expensive) QNAP raid housings here filled with drives - one is filled with standard consumer drives and the other with Western Digital "Red" (RAID) drives - both perform damn near identically and have pretty much the same MTBF.
That said, if you want RAID-on-the-cheap, look at UnRAID; several friends have been using that for years (since I started, before I graduated to more expensive solutions) and it has a number of advantages:
The drives don't need to be the same size, the only stipulation is that the parity drive(s) are the same size or larger than the largest drive in the array.
It runs on consumer hardware, you just need a reasonable motherboard (nothing too fancy) and a bunch of PCIe SATA cards (and a NIC, obviously)
It's very cheap
The software is now pretty mature and supports things like Docker so you can run containers with software like Plex Media Server or even ESXi and virtualise entire hosts on top of it (depending on how meaty your server is)
You clearly already have the hardware, assuming you can dedicate a machine to it, so it's a no-brainer to me. Run with dual parity and you can support the loss of two drives before losing any data - yes, it's not a backup solution, but it does significantly reduce the chances of data loss unless you ignore a failed drive.. (and despite supporting the loss of two I would
always replace a failed drive ASAP as the chances of another drive failing get significantly higher when the whole array is churning away for 48hrs solid rebuilding the parity drives)