> The cheapest one I own is $100, an old Vsonic GR7.

I don't think you're giving the recent years of IEM revolution credit.

All the $20 chi-fi like Chu, Wan'er, Zero have smoked the former $100ish classics like GR07 away.

$75–150 has been eaten up by Moondrop and others too. Shure's SE series and Westone, among others, have been eclipsed by this range.

I liked the $350ish IEM range myself earlier, which was considered just mid-fi earlier but now gets you pretty top-end performance.