Consider Christianity, volumes 1 & 2 are $11.55 each on Amazon.com
I don’t know how long this will last, but the new editions of both volumes, Evidence for the Bible and Christianity and Secularism are showing a price of $11.55 on Amazon.com. That’s a 32% discount. You should be able to get current pricing by running your cursor across the link.
To access their catalog pages here:
Evidence for the Bible (Energion Publications Catalog)
Christianity and Secularism (Energion Publications Catalog)