Kindle.

Althought there are free books to be found on Kindle - many of these are free for a very good reason!

Books can be expensive - even paperbacks so I now tend to use Amazon rather differently.
I am untroubled if a book be second hand and so I search out the volume I require, go to 'new and used' and more often than not, I am able to get a 'good' copy (often brand new) for just 1p.
Postage and packing comes in at about £2-86 - all in all, a book for up to three quarters off.
When you read as much as I do - this is an excellent way to go.
(I DO apologise to readers if I am 'teaching Gran to suck eggs'.