mishap Prices go from free up to over £10, but most are about £2 - £5. You can also get thousands of free books from Project Gutenburg, but most of those are out-of-copyright ones, excellent for classics and "literature" but also for quirky works you would never have come across in a bookshop. I believe there are other free sources, but I am still browsing Gutenburg so have not tried these.
Downloading from Amazon is a piece of cake - possibly too easy, as you can find yourself with a queue of titles waiting for you to read, and several chunks of a few pounds soon add up. As Annobel says, downloading a free sample chapter first is a good move. When you get to the end of that you can buy the rest very easily, and if it doesn't appeal you have wasted nothing..