Just out of curiosity, I looked up the availability of Aryeh Neier's book Defending My Enemy, which is one of the most influential books I've ever read.
I bought my first copy for five bucks. I ended up giving it to a friend when I left DC as a parting gift.
I decided that I wanted to read it again. I ended up spending $30 on a copy that used to being to a library. Any copy with the same cover as the first copy that I had was over $100.
Now, it's completely unavailable on Amazon. I can't seem to find anyone selling it except for one copy on eBay.
I'm not being hyperbolic in saying that this is one of the most important books ever published and, so long as we have public schools, this should be required reading.
Needless to say, I'm holding on to the copy I have. I just hope that more copies will be made eventually.