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?
It is easy to get to these drive self reporting data, but reading it can be tricky.
For Windows there are GUI tools like https://crystalmark.info/en/software/crystaldiskinfo/, that make all those values understandable even for people without much computer background.
For Linux the story is a bit different. Most current desktop environments do carry some functionality to read the S.M.A.R.T. data from the drives and display these data to the user. The user then has to find a way to interprete these seeminly random numbers. For things like the amound of written data to a drive (relevant for SSD) you have to pull out a calculator. Maybe there are also easily unterstandable GUI tools for Linux, I just haven’t found them.