In stock 12/22. Amazon
has the Western Digital WD Red Plus NAS WD40EFRX 4TB SATA3 64MB Cache 3.5" Internal Hard Drive for $85
with free shipping. eBay with Newegg
has it for the same price.
Features a 6.0Gb/s SATA interface, 3.5" form factor, and is designed and tested for 1- to 5-bay NAS systems.