Update: B&H now carries it for only $109 shipped.
Update: Adorama has dropped its price to $114.99 shipped
Amazon has the Western Digital My Book 4TB USB 3.0 hard drive for $124 shipped. That’s a current low price on this 4/5 star rated backup drive that is both great for backing up Macs and PCs as well as fast storage for media and other files. Connect it to an Airport Extreme or other USB-enabled router for a great NAS experience.
Bonus: If you have a few extra bucks, plunk down $144.99 and get a 5TB Seagate USB 3.0 hard drive bundled with Adobe Lightroom 5.0 from Ebay. Lightroom 5 alone is at least $75-$150 depending where you get it so it becomes a no brainer if you are in the market for both.
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You can get it for $109 from B&H: http://www.bhphotovideo.com/c/product/1077555-REG/wd_wdbwlg0040hbk_nesn_4tb_elements_external_hd.html