I've been following the news and it's amazing how SSDs are still progressing, a bit slower but similar to Moore's Law. Prices for Samsung SSD 1TB external USB products: - 2015 $600: Samsung T1 http://www.thessdreview.com/our-reviews/samsung-portable-ssd... - 2016 $430: Samsung T3 https://www.storagereview.com/samsung_portable_ssd_t3_review - 2018 $200: Samsung T5 https://www.androidheadlines.com/2018/12/samsung-t5-po…
I wouldn't use external SSDs as the price benchmark, since they had a big price premium over an equivalent mSATA SSD back then. For example, I bought a 1TB samsung mSATA SSD in 2015 for about $320 and it's enclosure for $15. The equivalent SSD today is about $150. So instead of a 3x price decrease in the past 3 years, it's more like a 2x price decrease.
Please feel free to create a similar list with 2.5", mSATA or m.2 drives, it probably is even more shocking.
The other awesome thing about those 3 I linked is that the interface also has changed: Micro USB 3.0 => UBS-C Gen 1 => Thunderbolt.