If you want to make an investment in rare books, move quickly to buy Alms for Jihad or Funding Evil: How Terrorism is Financed — and How to Stop It. You'll have to be quick, especially with the first. Amazon (UK) lists it as "currently unavailable", though it was published on 31st of March, 2006. The reason is that a Saudi banker, Khalid bin Mahfouz, who is named 13 times in the book, has sued the publishers, our esteemed Cambridge University Press, and they have caved in and not even contested the case. There is an apology on their website.
Mahfouz, who is a billionaire, has a liking for the libel court and has blocked publication of several books linking the Saudis to the financing of terrorism. The second book above was not even published in the UK, but he ordered multiple copies on Amazon.com and then brought his case. It succeeded in the UK courts, but the author has gained some protection in the US. She is Rachel Ehrenfeld, and she speaks about it to Hot Air here.