Server Part Deals is really good since they test the drives themselves. But even the used drives are on the verge of being unaffordable now. They increased the price of their 28TB re-certified drive last month by $120.

Well, you can take a walk on the wild side and for whatever reason this aggregator has a particularly robust set of sorting categories when it comes to hard drives. https://www.saleturbo.com/techdeals/

Caveat emptor, of course.