Newegg has the Western Digital Red 3TB NAS hard drive (WD30EFRX) on sale for $149.99. Shipping is free.
Western Digital Red WD30EFRX 3TB IntelliPower 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive
WD Red hard drives are designed and tested for compatibility in the unique 24x7 operating environment and demanding system requirements of home and small office NAS. With exclusive NASware technology built in, WD Red hard drive improves NAS storage performance by reducing common hard drive concerns in NAS systems including concerns for things like integration, upgradeability, reliability and cost of ownership that are experienced with a hard drive designed for desktop computers.