At MacMall, search for "9000191-R" to find the refurbished LaCie 4TB USB 2Big Thunderbolt External Hard Drive, model no. 9000191, for $359.99 with free shipping ($0.09/GB). That's the lowest total price we could find for a new unit by $209. It features data transfer rates of up to 327MB/s, dual Thunderbolt ports, dual cooling system, two hot-swappable disks, RAID support, and more.

A 3-year warranty applies, although it's unclear who backs it.