With these drives typically around $750/each, it'll be difficult if not impossible to find deals on 8 separate lots of _good_ used drives.
I can only afford them when I see an exceptional deal on eBay, and feel lucky to have found these I just got for $200/each. I strongly doubt I'll be able to afford to implement 1 drive per lot with my server like your warning implies would be a good thing to do.
It seems you'd have to buy them all new at different times of the year to be able to implement such a thing, which I certainly can't afford.