I run a repair shop, and one of the top computer repairs we do is to upgrade a spinning disk to a SSD.
A 240GB SSD runs $60-$65 these days, and is perfectly adequate for 99% of users. For that other 1% (which I include myself in) 512GB is adequate for 90% of those.
HDD -> SSD is the single most cost-effective upgrade most people can do to breathe new life into an older computer. Going from a spindle drive to a SSD in most computers decreases boot time from ~4 minutes to ~30 seconds. Browsers load faster, videos don't stutter as much, the computer runs more silently. These are the issues most people care about.
A SSD upgrade means a 2010 MacBook Pro now has another 2-3 years of life, which is awesome news to most of the people we serve (who are often college students just trying to make it through college without their computer dying on them.)
I hope to see this chart go to 0 in the next few years as SSDs continue to decrease in price; this doesn't mean much bad news for the "PC industry", just ancient relics of a bygone age finally dying (and/or becoming super-niche for things like archiving where data transfer rates don't particularly matter.)