I saw this earlier today on Amazon:
$299 6TB: Amazon.com: Western Digital Red 6 TB NAS Hard Drive 1 to 8-Bay 3.5-inch SATA 6, IntelliPower, 64MB Cache Internal Bare or OEM Drives WD60EFRX: Computers & Accessories
Same as the $300 Seagate desktop drive - Amazon.com: Seagate Desktop HDD 6TB 7200RPM SATA 6Gb/s 128MB Cache 3.5" - Internal Drive Retail Kit (STBD6000100): Computers & Accessories
$299 6TB: Amazon.com: Western Digital Red 6 TB NAS Hard Drive 1 to 8-Bay 3.5-inch SATA 6, IntelliPower, 64MB Cache Internal Bare or OEM Drives WD60EFRX: Computers & Accessories
Same as the $300 Seagate desktop drive - Amazon.com: Seagate Desktop HDD 6TB 7200RPM SATA 6Gb/s 128MB Cache 3.5" - Internal Drive Retail Kit (STBD6000100): Computers & Accessories