Diagrams can be even better, as they don't require lots of money to make, even animated ones. EDIT: And they can be just as clear and explanatory.
(Btw, I know I didn't try to collect to buy Bernhard, Xvimbi, etc. video cameras but you guys certainly deserve something too! It would be so nice if we could have a PF reunion and buy dinner and drinks for each other! )
I have learned so much more on this forum than I have contributed. I am still way on the paying side
What concerns contributions to CC's book, I know from other such projects that it is often not money that is needed, but time. That's why I think, if we want to contribute, we should do so in form of actions, not so much monetary donations. That could e.g. be typesetting, proofreading, translating, making drawings and videos, etc.