I first became aware of books by Thornton Burgess by browsing the Heart of Dakota curriculum website. The paperbacks aren't expensive -- you can get a boxed set of I think 5-6 titles for under $10 on Rainbow Resource -- but today I found more than 25 titles by the author for free on Kindle.
I don't believe these editions have illustrations (and I'm not sure if all the paperback versions do, aside from the covers). There are some titles that DO have illustrations, but those aren't free. Of course.
Still, free is free and it's a nice way to preview some books or have a bunch of children's read-alouds on hand.
I haven't decided how I'll approach Kindle books with the kids. I think they should have paper books for the most part. But for illustrationless read-alouds...I think a Kindle version isn't such a bad alternative (especially a free one).