There's tons of free OER (open educational resources) today; no need to shell out money and deal with the repetition and/or rote learning. Create/design your own.
I have posted many links to free resources on this forum and prefer low or zero prices to high ones. But I also expect authors, editors, and publishers to be paid for their work, just as I am paid for the intellectual work I do. Don't make a fetish of "free" or "open source". Wikipedia is great, but maybe it's also worth spending $70 a year to get access to Encyclopedia Britannica. Linux has a vital role in the computing infrastructure, but commercial operating systems are preferred by the vast majority of end users.
