Depends on who the publisher is, what they're publishing, & how big the book is.
If you're publishing something that needs to be in color, it'll cost more. If the book is of an abnormal size (either smaller or larger), it'll cost more. If you are going through a smaller publisher who can't obtain a good discount or doesn't have their own printing factory, it'll cost more. (You'd be surprised at how many people outsource to other factories.) The cost to PRINT a book is usually pretty low, to be honest.
It also depends on WHERE they're sending it. They have to pay for the trucks to distribute it to the various warehouse & locations, so if this is a smaller company or a company specializing in self-published books, it'll cost more to get the books to those warehouses & stores so the books can be sold.
Then on top of that you have the manpower. This is where a good sizable chunk of the book cost comes from because you have to pay the agents, the editors, & so on... Even minus the author royalties it comes out to a sizable chunk.
There's really no good answer, to be honest. I'll say that on average the author only gets about 10-15% in royalties, so that should give you an answer as to what to expect if you're wondering what the author should get. Depending on who you publish through & how influential you are, you could get more. If you self-publish then you might find that you are getting a lower percentage than people who are signed to companies such as Harlequin or HarperCollins.