My wife always tells me that I have to double everything whenever I estimate costs.
I brought these along for a specific purpose. I have three copies here. Unfortunately, I don't have enough to be able to give one to everybody.
These two books here were produced at no cost. We held a conference, we asked people to come to the conference, they paid registration fees for the conference, and part of the money was to give them a book at the end of the conference about what they talked about. So here are two conferences, two books, no cost.
The thing is that you can do things at very low costs when people care.