Most books are disposable to me: a tech book that is obsolete in a year, novels that are not worth rereading, a popular career or business book I read for context. $10/book is a little too much for something I'm only going to read once.
Someone once told me that if you can get _1_ idea from a book that changes you're outlook on things; then it's worth it, and I agree. I don't understand how people can say $10 on a book is too much; you can friggin' spend more than that on one meal!
EDIT: And as eru said, if you still think its too much, join a library.
I am doing no such thing. Sure, some of my purchase price will go back to the author and in aggregate with other purchasers they may be fairly repaid for their labours. But the book is worth whatever I was prepared to pay for it.
What you proposed was the Labour Theory of Value; a thing is worth the effort and talent put into it. Intuitively attractive, but it breaks down in economic practice. If instead you accept that things are worth what people will give up for them -- the Subjective Theory of Value -- economic analysis requires fewer epicycles and illuminates more phenomena.
I've spent > $100 on ebooks or courses, and they've been immensely helpful. I guess it depends on how much you're willing to pay for the value you get.
If you are reading for entertainment and a $10 book that 4 hours to read, that is only $2.50\hour. Seems like good value.
If it isn't for entertainment and you aren't deriving (syay) $10\hour of value out of it, then why are you doing it?