The second part (marked with a line) indicates when I was a guest on CppCast talking about Meson and the book. As an experiment I created a time limited discount coupon so that all listeners could buy it with €10 off. As you can tell from the graph it did have an immediate response, which again proves that marketing and visibility are the things that actually matter when trying to sell any product.
After that we have the "new normal", which means no sales at all. I don't know if this is caused by the coronavirus isolation or whether this is the natural end of life for the product (hopefully the former but you can never really tell in advance).
Thus, effective immediately, the price of the book has been reduced to €24.95. You can purchase it from the official site.