[michaelmrose]

If you use a filesystem that checksums you will know if the drive is likely bad and wont lose data unless local and backup go bad within the window required to get a replacement for whichever died. See zfs.

If your proposed backup solution is only used for periodic backups and isn't in constant heavy use 2 $50 1tb drives in raid1 would be quite secure against data loss and last years and for a bonus would be unlikely to be compromised by hackers or mined by the nsa for signs you are a terrorist.

If you project replacing the drives every 5 years your annual cost could be $20 and your up front cost no higher than dropbox. Its even entirely likely that you could get by with a single drive for a annual cost of $10.