From what I've experienced and heard, let's say your non-fiction book is derived from an article you've just published in Vanity Fair, Esquire, the New Yorker, or the NY Times Magazine, you could easily be looking at a six figure advance.
On the other hand, let's say you've never published so much as an article before, then you might pull down as little as $3000 at a major house, and nothing at all except royalties at a very small publishing company.
If you're track record is somewhere in the middle, I think the middle range would be $10-$40,000, depending on the strength of your proposal and the marketability of your concept.