Adorama on eBay is offering the Seagate Expansion 4TB USB 3.0 Desktop External Hard Drive (STBV4000100) for only $109.99 shipped. That’s $60 off the list price and the lowest we’ve seen it go. Amazon sells it for $120 currently and customers there gave it 4/5 star reviews.
The Seagate is USB 3.0/2.0 compatible so you don’t have to worry about hardware compatibility issues.
The 5TB version is also available for $120 shipped from eBay