I did a survey of the cost of buying hard drives (of all sorts), CDs, DVDs, Blue-rays, and tape media (for tape drives).
Here are the 2019-07 results: https://za3k.com/archive/storage-2019-07.sc.txt
2018-10: https://za3k.com/archive/storage-2018-10.sc.txt
2018-06: https://za3k.com/archive/storage-2017-06.sc.txt
2018-01: https://za3k.com/archive/storage-2017-01.sc.txt