Looks like I'm actually going to beat @kenubrion to the punch for once!
Red Rising by Pierce Brown, a book I haven't read but is generally well-regarded, is $1.99 on Amazon. Here's the link for the Canadian website, I know the deal is there on the US site, too. Not sure about other regions.
Last month, I had recommended signing up for Tor.com's eBook of the Month Club. Well, in case you haven't, you should probably do so. This month, in anticipation of the upcoming release of the first Murderbot novel, the Club is making all 4 novellas in Martha Wells' Murderbot series available for free.
Each book is only available for 24 hours, though. Today is the first book (All Systems Red), and the next 3 will be over the coming 3 days.
I'll quote my original comment below which links to the sign-up page.
Just thought I'd mention, in case people were not aware, that you can sign up for Tor.com's "eBook of the Month Club" and basically get a free SFF ebook every month. I've had it for quite a while now, and the books you get can vary from known, award-winning authors to newbies, so it can be hit-or-miss. But, hey, it's free so what do you have to lose?
This month's selection is Redshirts by John Scalzi, which won the Hugo for Best Novel in 2013.
Yet more plugging for the eBook Club. On May 4, Tor will be giving away free copies of The Way of Kings by Brandon Sanderson. So if anyone wants to read it, but hasn't gotten around to it, now might be a good time to sign up.
Also, a bunch of SFF books are currently on sale for $2.99 on Amazon:
I just bought this yesterday. I was surprised when I went through Amazon's Fantasy Bestseller list and saw this pretty high up; until yesterday, I literally wasn't even aware of either the series or the author. Never heard anyone mention them.
Robertson is a very prolific author and writes excellent fantasy and sci-fi. He has written several multi-volume series in both genres. Check out his voluminous author page https://www.amazon.com/Edward-W-Robertson/e/B004NW3PYY
He is a rare writer who puts out huge numbers of books yet maintains a very high quality of work as well.
The Magicians by Lev Grossman (Book1 of The Magicians Trilogy), a book that is generally well-regarded but that I personally despised, is $2.99 today.
All Systems Red by Martha Wells (the first in the Murderbot series of novellas) is for $1.99 (for those who didn't get them for free from Tor.com last month).
The Monster Baru Cormorant (the second in The Masquerade trilogy) by Seth Dickinson is for $2.99. I have this series on my TBR list, but haven't gotten around to it, yet. Supposed to be well-written, though. Has anyone here read it?
Also, if you're a fan of the cult leader founder of Scientology L. Ron Hubbard, his Battlefield Earth is available for $0.99 for those who like crap. I refuse to share the link.