Interesting, very interesting, at roughly $25-30 for a 500Gb drive, (let's call that typical for a workstation PC) I think rotating platters might be made obsolete like CD's have generally become.
I think at that price point (and we're almost there! - $38.99 retail FS for a 512GB lesser-tier SATA SSD recently), you will start to see a mass-exodus away from HDDs, at least in entry-level OEM PCs that previously shipped with 500GB or 1TB HDDs.
Part of the problem, although it's getting less so, is the "old codgers" (think, PHBs from Dilbert), that spec out mass PC purchases "by the numbers", and see 1000GB (1TB HDD), versus 500GB (SSD), and think that the higher number is better.
IMHO, and I've been practicing what I preach for quite a few years now, even with budget builds that I do - I use a (small, if necessary) SSD for the OS, and (optionally) a 1TB or 2TB HDD (usually for game storage).
On my personal rigs, I don't have overly-huge SSDs, actually, because I have (several) NAS units, that I use for backup (smaller primary SSDs make backups faster), and use large (8-10TB) HDDs for NAS bulk storage, for storing things. Sometimes I'll slap a large-ish HDD into a client box, if I want the ability to do local backups, or have a local archive, for downloads and ISOs and whatnot.
But back to the original point, the size of a primary OS SSD, that can stand alone, without a supplemental HDD installed, these days, for basic gaming and budget boxes, I think, a 500/512GB SSD fits the bill nicely. And at under $40, won't break the budget. Once they hit $30, OEMs will notice and switch.
And for NVMe PCI-E SSDs, I like the 256GB Patriot Scorch PCI-E 3.0 x2 NVMe drives, for $29.99 on sale, and the 1TB and 2TB Intel 660p NVMe SSDs (QLC on those), for $87 and $177 respectively. Performance isn't horrible with those QLC drives either.
PCI-E 4.0 x4 NVMe SSDs are finally hitting the streets too, but they carry quite a premium ($230-250 for a 1TB). Might be a while before I upgrade to those. Need a PCI-E 4.0 mobo, which means, an X570 AM4 board, and a 3rd-Gen Ryzen CPU. (3000-series Ryzen APUs are actually 2nd-Gen, and only a 12nm shrink of the original 2000-series 1st-Gen Ryzen APUs, and DO NOT support PCI-E 4.0, unfortunately.)
So, beware of 3000-series Ryzen APU combos with an X570 board, because if you get that combo, you WILL NOT be able to run a PCI-E 4.0 x4 NVMe SSD, at PCI-E 4.0 speeds, you will be limited to PCI-E 3.0 speeds.
However, conversely, if you have an existing B450 board, or X470 AM4 mobo, and drop in a 3rd-Gen (3000-series) Ryzen CPU, you might gain PCI-E 4.0 support for the primary PCI-E x16 slot, and the x4 primary NVMe socket. Depending on mobo support, wiring / layout, and testing. At least, there was talk of retrofitting PCI-E 4.0 onto existing X470 and B450 boards, that could physically support it and be tested for proper support. (Generally, means that the primary PCI-E x16 slot, and the primary PCI-E x4 NVMe socket, are wired directly to the CPU, without excessive trace length or PCI-E splitter/multiplier chips.)