Baker Family Adventures Book (series)

Hi Everyone:
We have the first 3 of the Baker Family Adventures Series…..and the 4th one just came out (YEAH)! However, I have only seen it for sale for $15. That is far too steep for a paperback book IMO> Wondering if anyone has seen them cheaper anywhere?

This is the link to the first book in the series in case you are not familiar. My girls don’t love reading, as most homeschooled kids do….but they LOVED these Christian adventure books.

http://www.amazon.com/Summer-Suspense-Baker-Family-Adventures-ebook/dp/B00PVZHPH0/ref=sr_1_2?s=books&ie=UTF8&qid=1448072155&sr=1-2&keywords=baker+family+adventures