Their books are on sale on Amazon all the time too and often have an additional Prime discount - I got a bunch of them several months ago for around $15 each. Just be careful because there are several editions of some of them with slight changes in the name but almost no actual text changes - if the description sounds like it might be the same thing as another one, it probably is, but it won't straight up say that.

Also, most of the "cookbook" ones seem to be good resources if you are just looking for a solution for something, but they rarely explain they "why" - they are very much of the "click this,", "enter 5," "click this" school, so they are not good learning tools for the beginner in my experience.