Well, Cherie just tweeted that the Kindle edition of the first book, Boneshaker, is available right now for $2.99. I see Clementine is $4.99. So, you can check out the beginning of the saga for just a few bucks, and if you love it, the third and fourth books are ready and waiting for you.
I should add that you don't need a Kindle in order to read Kindle e-books. I read them on my iPhone or iPad, and you can also read them in a web browser on a computer.