I had a disk in my ZFS pool (a relatively tiny one, among the kind of people who have a home ZFS RAID5 array) go bad earlier this year and bought a used disk for the first time ever. Never even considered it before.

Still cost me as much as a pair of new drives the same size that I bought to transition from mirrored pairs to a four-disk RAID5 array about 16 months earlier. Like, god damn it was expensive.

A new disk would have cost me almost as much as all four disks did, originally.