Once you've had the opportunity to read some or all of the book and download some of the code, consider paying for it.
You can set your own price. I've opted not to set a fixed or suggested price. Instead I'll let you tell me how much the book and code are worth to you, and eventually we'll see whether the cost of keeping them up to date is worth it to me.
Everyone who pays will receive a copy of the book in PDF format.