You like the book but dislike its price? You want to assign it to students but afraid the price-tag is too high?
Consider renting it! You and your students can have it, in print or as an e-book, for $20 or less for a semester.
See for example here for rentals of the print version (http://www.ecampus.com/catholicism-today-introduction/bk/9780415719438&pos=1), and here for rental of e-books (http://www.coursesmart.com/catholicism-today/evyatar-marienberg/dp/9780415719421).