Walmart offers the Toshiba 1TB Portable USB 3.0 External Hard Drive, model no. PH2100U-1EWR, for $79 plus $2.97 for shipping. (Free Site-to-Store is also available.) That's $0.08/GB and the lowest total price we could find. Sales tax is added where applicable. The enclosed 2.5" hard drive features a 8MB cache and runs at 5400 rpm.

Update: It's now available for free in-store pickup at select locations.