Western Digital offers its factory-refurbished Western Digital 1TB My Passport Air Portable USB 3.0 External Hard Drive, model no. WDBWDG0010BAL-NESN, for $39.99 with free shipping. That's $10 off list and the lowest total price we could find. It's designed to work with Apple MacBook Air and features support for Apple Time Machine, password protection, and hardware encryption. A 6-month Western Digital warranty applies.