Are you looking for cheap and deep HDD storage? WD's 12TB Elements external hard drive is now a mere $174.99 with free shipping for Prime members, which is a savings of $75 over the normal MSRP (not counting shipping).
That's a great deal for Prime Day, especially considering that this drive is shuckable - meaning you can pry it out of the external casing and use it in your desktop PC. Proceed at your own risk, though: Shucking the drive voids the normal two-year warranty, but you do get a capable drive for far cheaper than you normally would. For instance, drives with a similar capacity often retail around $375, so the practice is common among data hoarders.
WD's 12TB Elements external hard drive is now a mere $174.99 with free shipping for Prime members at Amazon, a savings of $75.
When it comes to cheap and deep storage, external hard drives offer the best price-per-GB of storage you can find on the market. You can also shuck the drive and use it in a desktop PC, but that does void the warranty.
If you're looking to go the traditional route and use the drive as an external device, you're still getting quite the bargain. The drive connects to the host PC via USB 3.0 and has a relatively sluggish 5,400 RPM drive inside, but that's fine for bulk secondary storage devices and delivers ~100 MBps of throughput via the USB cable.
The drive also comes with a power adapter, but it's a fairly standard affair for this type of device.
This drive is fine for bulk data storage, like videos, pictures, and backups, but heck out our Prime Day SSD deals page if you're in the market for much speedier devices for gaming and other high-performance workloads.