Seagate 880GB 2.5″ USB Portable Drive & $10 Best Buy Gift Card for $119.99 shipped. Add both the 880GB portable USB drive and the $10 gift card to the cart. The discount will appear automatically as shown in this screenshot. It is USB powered and does not require an external power supply. This drive is smaller than 3.5″ external drives, making it more convenient. 880GB is currently the largest capacity for a single 2.5″ portable USB-powered external drive. Most places have it for about $139 without the bonus gift card.