Buy via eBay offers the Western Digital 3TB My Book USB 3.0 External Hard Drive for Mac, model no. WDBYCC0030HBK-NESN, for $99.99 with free shipping. (Groupon offers the same.) That's the lowest total price we could find by $19. It works with Mac systems right out of the box and can be reformatted for Windows. It features USB 3.0 and 2.0 ports and password protection. Deal ends March 2.