My first book, Geometric Algebra for Electrical Engineers is available in the following formats. In black and white, for $15.50 USD (softcover), or $23 USD (hardcover.) As a FREE (color) PDF. As a leanpub e-book for $5+ (set your own price). There is also a discussion forum for this book on leanpub, albeit unused. As latex sources (see below.)
The softcover