I noticed in arcadata's wonderful May affiliate thread (
https://www.mobileread.com/forums/sho...d.php?t=177087) that there are a bunch of HarperCollins mystery series backlists now with $3.99 prices, and even $1.99 for a few (mostly first-in-series) titles. See posts 3, 5, 9, 12, 13, 14, 21, 24, and 26 in that thread.
This is much closer to where I think backlist pricing should be, although $3.99 is still not cheap enough for me to replace DTBs I already own, unless from a particularly loved series. But $3.99 is definitely a price that I would buy backlist e-books at, in preference to buying used or checking out from the library, if I were to find a previously unknown (to me) series that I liked and didn't already own in DTB.
Still, I'm tempted to go ahead and buy a few in some one of the series I like (although none are ones I love), to encourage this sort of pricing on HC's part...we'll see how rich I feel tonight...