Why $3,000? That's clearly not enough to pay for writing a book; is it just to gauge demand?

It is based on what other programming books on Kickstarter ask for and from my past experience. Advances from traditional publishers are not that much more than $3000.

The majority of successful programming books on Kickstarter raise anywhere from a few thousand up to around $10k. The lucky few raise $20K to $100K or more.

Since I enjoy writing programming books, I don't need it to replace my income just supplement it.