I buy all of them.
I don't find most of them expensive, but that's subjective. Also, cheaper doesn't mean less valuable and I'm not a fan of the Programming Wisdom books, since they are expensive even to my mind because only little of each book is of any use to me.
Before purchase, I check if the information is readily available on the Internet and try to figure out what the book might be revealing which isn't readily available. If I buy a book I'm always thinking that, compared to alternative learning solutions like University or Seminars, books are comparably cheap. And the value it adds to my knowledge base over time can't even be expressed in money.
In over 15 years I've spent about $5,000 on educational and programming books. If I hadn't done so, I might not be here, I might not have had the great jobs I had. That's how I look at it. Money is a short term thing you best invest into yourself. Books are a very cheap way to learn from experts in their fields.