The Kindle currently on sale on Amazon for $1.99. There are two interesting — but too short — chapters on breathing, as well as many other topics. I've read four chapters so far, they are very good primers, good enough to get you interested, if you're curious, and not too technical to get you bored. I knew a lot about most of the stuff I've read so far, so I found it a quite easy read. I like the fact that each chapter is self contained, and you don't need to read the book from cover to cover.

Very good value for money.