Green Tea Press (by Prof. Downey) has a donate button. That's probably a more efficient means of supporting the project than buying the book, considering all the middlemen.
Oh my ..., was skipping too fast through the page and didn´t see this, and also didn´t realize what he exactly is doing with his Textbook Manifesto etc.
Ok, the Paypal-Link is a no-brainer for me now. Thanks for pointing out the obvious.