But that wasn't the case here. To the original poster, you might enjoy looking at the blogs of writers Jim C. Hines and John Scalzi. They don't write tie-in, but they lay the numbers all out there every now and again.
Someone mention Scalzi?
Here's something he wrote on the book deal; of course, from a non tie-in perspective and a little tongue in cheek:
http://whatever.scalzi.com/2004/09/08/the-real-world-book-deal-descriptions/
And some hard numbers on the "Shitty Deal":
http://www.scalzi.com/whatever/002869.html
There's also other publishing perspectives from the author's view from the gallery as well on his blog.