It occurs to me that if I offered as a prize in the juvenile diabetes auction "Your published book as the topic of discussion in Evil Editor's September Book Chat," it might raise a few bucks. It would probably be one of the one-day auctions.
However, it also occurs to me that it would annoy me to spend money to get my book featured only to have very few people read the book and show up. If the book were an unknown quantity, how many of you would be willing to get it and read it? I don't want to declare that many people will participate and more will read the chat transcript and pick up the book if the chat makes it sound good, only to be proven a liar.
This almost certainly would ensure that the author would show up, if nothing else.