You could just go with two 10TB drives for $169 each (shucked drive from Best Buy) and do Raid 1. Don't need to get more complex than that.
This is the lowest these drives have been, and they have a WD Red/White inside if you "shuck it" (pull the drive out of the external enclosure).
Very cool! I am lucky and I get education pricing. I might have to dig into this a little deeper.
A video on shucking an 8TB Easy Store Drive
Should be similar for most of the Easy Store Drives.