In Canada at Kobo (presumably matched at other Canadian retailers), a number of titles are going dirt-cheap as part of the Victoria Day long weekend sale, still good for the next couple of hours (sometimes Kobo has a nasty habit of expiring sale prices an hour or two before midnight Eastern Time, though). These are really good prices, especially if you like Scandinavian crime.
A number of titles by Sweden's Liza Marklund are just $1.99 each from Random House Canada. This is pretty much the lowest I've ever seen them, and I will be buying the lot shortly.
Norway's Jo Nesbų has two of the latest of his crime thrillers for $4.99, and an omnibus edition of three of his Harry Hole novels (#7-9, IIRC), for just $4.99 (regularly somewhere in the $25 range). ETA: I should note that the omnibus, which I bought and
read years ago when last it was on sale at this price, is a good jumping-on point for the series, as the books immediately prior wrapped up a significant story-arc, and the first book in the omnibus starts a new direction for the character and introduces new characters to his supporting cast. Also, FWIW, I didn't find
Blood on Snow, 1st novel of the new series, all that compelling
when I read it from the library and would personally wait for an even lower price, but maybe the 2nd is better.
Sweden's Lars Kepler has several titles in the Joona Linna series at $2.99-$4.99. (The omnibus edition of the #1-3 has previously been on sale, so you may need to check your records.)
There's also some of Alan Bradley's Flavia de Luce series at $2.99 each, and Linwood Barclay at $3.99, and some Maureen Jennings (author of the Murdoch Mysteries series that the popular TV show is based upon) and Peter Robinson et al. at $4.99 or less.
Linkage:
Page-turning thrillers & mysteries
Also, for the Francophones, Kobo Canada has a sale (not limited to the long weekend, as far as I can tell, but probably just until the end of the month), on French-language mystery/thrillers, both native and translated. I'll note that it includes titles by Sweden's Vivica Sten and Spain's Antonio Garrido at a significant discount. These authors' particular sale books have been published in English translation by Amazon's AmazonCrossing imprint, in case you wanted to pick up some language-practice fodder at a low cost.
Linkage:
Polars en promo ą plus de 50% de rabais!