For what they say is today only as part of a 1-day Christmas deal on assorted fiction and non-, both Amazon and Kobo in Canada have a number of discounted sfnal titles from major publishers on sale for $3.99 or less (some prices may also be available in the US):
In Canada only, it's just $3.99 for Simon & Schuster's 50th anniversary edition of Ray Bradbury's vintage classic
Fahrenheit 451, which has extras like an introduction by Neil Gaiman, and what looks like a substantial set of supplementary analytical essays and bonus materials in the back.
There's also a similar 50th anniversary edition of Joseph Heller's literary fiction classic
Catch-22 for the same price if you like annotated editions. These don't seem to be discounted elsewhere; both $11.99 in the US, and eReaderIQ says the lowest the Bradbury price has gone is $4.36 USD.
For $2.99, there's also the 10th anniversary edition of Neil Gaiman's
American Gods enhanced with bonus materials and the author's preferred text (the long-ago HarperCollins BookPerk Humble Bundle only had the regular edition), what looks like Neal Stephenson's latest novel from 2017, a seasonal satirical fantasy by Christopher Moore, YA fantasy by Victoria Aveyard, etc. Those looked like they were available in the US when I spot-checked.
There's also a rather nice-looking fully illustrated edition of Neil Gaiman's YA short story
The Sleeper and the Spindle for $1.99 in Canada & the US, but this is a regular HarperCollins weekly markdown rather than a special holiday sale promotion.
And Kobo Canada's special 12 days of Xmas Daily Deal is for Diana Gabaldon's Outlander universe (including the Lord John mysteries) short story collection for just $4.99 CAD ($14.99 in the US), collecting the previous shorts and novellas and adding new ones as well:
Seven Stones to Stand or Fall
Linkage for the lot of the sale pages @
Kobo Canada &
Amazon CA