Seagate Backup Plus 4TB USB 3.0 Portable Hard Drive for $79.99 shipped after applying coupon code GMA30. Here is a screenshot for reference. This portable USB drive does not require a separate power supply and is smaller than most of them, making it more convenient to carry around. USB 3.0 interface is compatible with USB 2.0 and able to transfer data at 3x faster by using USB 3.0. Most places have it for about $109.