Amazon offers Mark Twain's The Adventures of Tom Sawyer Kindle eBook with Audible Narration for free. (Check the box labelled "Add Audible narration to your purchase", located under the "Buy now" button.) That's about $4 under what you'd pay for a physical copy of any version of this book at your local store.
Don't need the narration? iTunes, Google Play, and Barnes & Noble charge the same for electronic copies.