I built my "NAS", which is just a normal computer with no GPU but 3 hard-drives in RAID 5, for $400 + storage cost. It is much more powerful that any NAS, even thousands of dollars ones, I'm not too sure at what cost (power consumption maybe?).

I don't understand why people would go with an actual pre-built NAS from a manufacturer over my approach. It's always a complete rip-off.