Newegg offers the Western Digital 6TB Red Serial ATA 6Gb/s 3.5" Internal NAS Hard Drive for $219.99. Apply coupon code "EMCRFBD25" to cut it to $209.99. With free shipping, that's tied with our October mention as the lowest total price we've seen. (It's a current best by $10.) Designed for NAS systems, it features a 64MB cache.