If you're interested in Poisoned Pen Press' mystery lines, Kobo US' weekend sale, still good through today, December 18th is for 3 for 2 on select mystery/suspense titles, which appears to consist of PPP's mysteries, which seem to rarely go on sale these days and are VIP discount eligible, so 33% off seems a decent deal, provided you can find enough titles you want with matching amounts. Prices start from $0.99 up, and generally tend to go to around $6 or $7 pre-discount, but there are enough lower-priced early-in-series titles at the $3 mark that you can try to see if you'd be interested in the rest later on.
Authors include Australia's Kerry Greenwood (Phryne Fisher historical mysteries, basis of the TV series), Canada's Vicki Delany, vintage British mysteries from George Bellairs, and many more from around the world. I've personally enjoyed and would recommend Priscilla Royal's medieval mysteries, Mary Anna Evans archaeological artifact mysteries, Beverle Grave Meyers' 18th C Venetian opera mysteries starring a castrato, among others.
ETA: There's also some genre-related non-fiction, and
Bound by Mystery: Celebrating 20 Years of Poisoned Pen Press is a nice-looking anthology which features a goodly number of newly-written short stories from their stable of authors, some in their popular series, and others introducting new characters.
Main promo page, with categories:
Mystery & Thrillers,
Police Procedural and Hard-Boiled Mysteries,
Amateur Sleuths and Private Investigators,
Traditional Detective Fiction,
Women Sleuths,
Historical Mysteries,
Kids & Young Adult Mysteries