Lisp is awesome, but I wish more places used regional pricing for online purchases. It's kinda crazy paying 40 dollars for an ebook since it's almost 1/5 of our minimum monthly wage (Brazil)
When you can’t afford you can download pirated version and donate if you feel that the book gave you value.
2021 was the 2nd year in a row that there was sales on Apress where they throw out great Lisp books for 6/7/8 Euro printed or digital. Subscribe to r/lisp or r/common_lisp and you will get the news.
Books like this sometimes feature in humble bundles.