Newegg offers the Western Digital 3TB Red Serial ATA 6Gb/s Internal Hard Drive, model no. WD30EFRX, for $109.99 with free shipping. Outside of the mention below, that's the lowest total price we could find by $11. (We saw it bundled with an $18 Rakuten credit for $12 less in August.) It's optimized for use in NAS systems and features a 64MB cache.
Note: If you haven't yet, use Newegg’s Android app and pay using Google Wallet to cut it further to $94.99. (This discount can only be used once per account.) That's the lowest total upfront price we've seen this year.