Academic books with a small print run (hundreds rather than thousands)? Or non-fiction books for a larger audience?

I'm afraid to say that small-run academic books aren't going to make you rich. Depending on how well known an author is and how big the press, the advance might even be as small as US$1000 (eek). I guess that's one reason academic books tend to be written by people ensconced in academic jobs and not those who have left the academy. The reason to write an academic book is more to further your career and to increase the knowledge available in your field than for direct personal gain, but I'm sure you know that already!

As for nonfiction for a wider audience, well, if you're Harold Bloom or you're writing something high-profile like the Cambridge Guide to Whatever, you could get a five-figure advance (lower for Cambridge, higher for Harold Bloom). If you're writing highly commercial non-fiction (I want to write a book called Eat and Grow Rich--can you imagine the sales?) for a major publisher that's going to put a lot of time and money into publicity and expects worldwide sales, the high five or low six figure range might not be out of your grasp.

If you're offered a low advance and your publisher refuses to bump it up, you can always try to negotiate a favourable royalty structure. That way if sales exceed what the publisher is anticipating you'll get a little more money out of the deal.

Anyway, these figures aren't set in stone, it's just what I've gathered from speaking to a few agents and reading the publishing press. Perhaps I'm estimating a little too low on the worst-case academic side, but I'd be surprised if I was very far out.

Right! Well, a popular non-fiction book on some intellectual subject (i.e. NOT Eat and Grow Rich), depending on publisher, might realistically get you an advance in the high four or low five figure range. If the publisher saw you as the Next Big Thing and your subject as having wide appeal (like a biography of some eccentric historical figure, which have been v. popular these last few years) you might get upwards of $20K. If you DID turn out to be the Next Big Thing with sales to match, future books would probably make considerably more if you were with a big commercial publisher.

If I see any examples of relevant reported deals in the specialist press I'll pass them on to you. x

Oh, I forgot to say, if you're writing popular history or other non-fiction, get yourself a literary agent. That person will try to sell your book in various countries and formats to bring you a larger revenue stream. Yes they will take a slice of your book income (usually 10-15% for domestic rights and 15-20% for overseas and translation rights) but they'll help you make a lot more money than you would otherwise--and many publishers won't even consider unagented books, or will take many, many months to look at proposals.

An excellent book about the process of getting an agent and getting your book published is Carole Blake's From Pitch to Publication. Blake is a highly successful UK agent herself.

And hell, if you're writing for someone like Brill who prices their books way out of the range of most people you can make better return asking for a slew of extra copies for yourself - if the book is priced at $125, and you ask for another 20 or 30...