Found the sale that goes with all the HarperCollins price-drops upthread.
“The age of the anti-heroine” at up to 80% off runs until May 29th @ Kobo CA, and features all sorts of mystery/suspense novels with female protagonists by authors of all genders, including classics like Agatha Christie, YA like Norma Fox Mazer, and more, at $4.99 or less (mostly in the $2-3 range).
Main page, with categories:
Reads That Will Keep You Guessing,
Women Sleuths,
Heart-Pounding Romantic Suspense,
Police Procedurals,
Thrilling Reads for Young Adults,
Unputdownable Thrillers