There's a bunch of Linux ebooks you can get from
Humble Bundle right now for as little as $1.31 CAD.
Part of the purchase price goes toward EFF and Let's Encrypt, two worthy tech causes and its adjustable how much does. Let's Encrypt protects privacy for numerous websites that might not be able to afford it including ours. The Electronic Frontier Foundation exposes privacy exposures by major corporations in their user technology as well as hosting tools that check and make your browsing more secure and private.
The attached image shows the middle-tier for under $25 and just the top 3 books. There are 13 others listed on the website. The bottom tier has 3 books.
While I'm sure some of the books aren't the most recent, I've never seen them offer anything that wasn't worth its price.
