When my co-author and I signed the contract, we each got a low-to-mid three figure advance on the royalties. That means that they gave us money up front, but it was to be deducted from our later earnings. Then upon submission of the completed manuscript, we each got another low-to-mid three figure advance on royalties. When the book was published, we each received one hardback copy and ten paperback copies of the book, plus the offer to buy as many copies as we want at 30% off the list price. Then, for as long as the book is in print we get 10% (5% each) of the money Routledge receives for paperbacks that are sold (and 7.5% of the money Routledge receives for hardbacks).
The book came out in July of 2010. And evidently it did better than was expected, because it sold out of the first printing sometime in January. The first printing was 1200 copies, so we're not exactly talking about a NYT best-seller. Its primary market is as a textbook, and there were a few schools that adopted it for the spring semester. At one point during the holidays, it made it up to #34 on Amazon's top 100 books on religion (which was something like #24,000 for its overall best sellers). The price then was down to about $24 (which is cheaper than I can buy them from the publisher), but currently it's at about $38 on the site. I could make you a deal on a signed copy if you're interested!
Anyway, my portion of the royalties (after deducting the two advances) for 2010 was in the mid three figures. When you add all of those payments together, I'm up to the very low four figures (not counting decimal points!) in money earned on this project. I estimate that I have significantly more than1000 hours invested in working on this book, so we're talking less than $1/hour. Such is the reality of academic publishing. In a future post I'll explain what drives us to do such things.