I used to think that way too, then realized, who gives a fuk if using 321 backup method and have a cheaper spare on hand doesnt matter. Also this isnt enterprise, where i wouldnt even think about getting used.

Serverpartdeals is very reputable seller of refurb drives with low usage. Buy few in size you qant put them in a zfs or raid1 and move on with your life. However just make sure you have error chexking and drive tests on to find faulty drives and alerts you have tested working before you set it and forget it.