The hardcover price I see on amazon.com is $56.16, Kindle for $50.68. Amazon.fr still has it free, but won't let me buy it from the UK. Amazon.de has it for €50.94. I'm betting this really is a glitch currently in the process of being fixed.
You're right, it probably was a glitch. I looked again today and now it's $52.89 for the Kindle edition. :(
**** DEAL OVER: As of 20120611.
Another free kindle I thought some might have interest in. I haven't read it, but the first review was glowing and looked relevant.
First Amazon Review:
> Five Star Final; Excellent; A "must read" for any "student" of brain-behavior relationships
http://www.amazon.com/gp/product/B005DKQQG4/
UPDATE: Still free at the US amazon at 2pm eastern time. Reports that it is not free at the UK site, which I verified. Since I can log in to the UK site from the US and see the price, I assume people in the UK could sign into the US site and buy it. If anyone gives that a try, let me know and I'll further update the top level.
UPDATE: Free at amazon.fr. Can buy at the US site from the Netherlands. Can't buy from FR or US sites from UK.