Amazon offers the Seagate 4TB Backup Plus USB 3.0 External Hard Drive, model no. STCA4000100, for $159.99 with free shipping ($0.04/GB). That's the lowest total price we could find by $19, although it was $7 less a week ago (since expired). Sales tax is added where applicable. It's compatible with Windows and Mac and features two backup scheduling options, social network sharing, and more.