Newegg offers the Western Digital My Cloud USB 3.0 6TB Personal Cloud Storage NAS, model no. WDBCTL0060HWT-NESN, for $276.99. Apply coupon code "VCOJAN25" and checkout via Visa Checkout to cut that to $251.99. With free shipping, that's the lowest total price we could find by $8. It features Gigabit Ethernet and free apps for uploading and accessing files.
Note that the coupon only applies once per account.