NeweggBusiness offers the HGST Deskstar 4TB NAS Serial ATA 6Gb/s Internal Hard Drive, model no. H3IKNAS40003272SN, for $154.99 with free shipping. That's the lowest total price we could find by $10, although we saw it for $20 less in December. This 7200rpm hard drive is designed for NAS systems and features a 64MB cache.
Note that this is the bare drive.