I just browsed eBay a bit and saw that older, used SAS drives can be had pretty cheap - 30€ for 4TB, but of course rather old drives, sometimes 10 years old.
Now, I wouldn’t expect ultra reliable, ultra fast, super cheap drives here. But this offer seems compelling, even buying a spare drive for higher redundancy would still be pretty cheap.
Question is: am I too optimistic here? Are these drives bound to fail within 3 months?
Hmm, I would only purchase them as a third (or more) layer of redundancy, or maybe for storing things like ripped media that could just be re-ripped (or re-torrented) should the drives fail. I would not trust them for anything important since you have no idea what kind of environment they were in for all those years.