The Biggest cost is in the ability to access it through a network system, so I separated the two cost elements.

First purchased a 4 TB My Cloud (Network Archiving System) they come in 2, 3, 4, 6, 8 TB sizes and of course ran out of storage.

Then purchased a 8 TB USB 3.0 external hard drive they come in sizes between 3 TB and 20 TB. Plugged it into one of the two USB ports of the My Cloud and I now have a 10 TB network archiving system and can add a another or larger hard drive when needed.

If you were thinking of buying a Network Archiving System check the prices per terabyte if you configure it as described above.