There is one first-time-free paleo book:

The Cooking Caveman: How to Lose Weight, Eat Healthy, Create 
Mouthwatering Paleo Recipes, and Piss Off All Your Friends! by Jeff Nimoy
http://www.amazon.com/dp/B00AAKBZF4

Then this is another first-time-free book:

Best of Grain Free Meal Plans, Volume 1: A cook book for those 
following grain free diets by Cara Faus
http://www.amazon.com/dp/B0089CLMJ4

There are also a few that were also free in the past. See them here:
http://www.amazon.com/s/rh=n:283155,k:paleo,p_n_feature_browse-bin:618073011&sort=price