The subject matter covered is so ancient & timeless that there are plenty of cheap "dover reprint" type books, and even books in the public domain. The spirit

The subject matter covered is so ancient & timeless that there are plenty of cheap "dover reprint" type books, and even books in the public domain. The spirit of open access / open source in relation to textbooks is commendable of course, but I don't think $100 is the benchmark here.