How much money is a book really worth? Is it the $25 to $30 publishers typically ask for the hardcover edition? Is it the discounted price plus shipping that an online retailer charges? What if there’s only a Kindle edition you can buy, for 99 cents? Is that same book worth nothing on days when it’s given away free? Is it even correct to call such a digital entity “a book”? The easy answer is that a book is whatever readers decide is a book, and it’s worth whatever they’re willing to pay for it.

Right now, the situation is fluid, to say the least. Scarcely a minute passes in the books corner of the Twitter feed that someone doesn’t predict—gleefully—the demise of legacy publishing, and with it the end of the book as we know it. New authors, previously locked out because they didn’t have agents or publishers, are now hawking their self-published books on blogs and in the social media. Most will be disappointed by meager sales—but then the same is true in legacy publishing. Books are always a long shot.

Since nobody knows how all this will turn out, let’s ask a different question: what does a book cost? Here the answer depends on what kind of book you’re talking about. It costs time and effort to write a novel or a memoir or a book of poems—not an insignificant investment, but no cash needed. Nonfiction books—especially research-intensive nonfiction on subjects like biography, history, science, social science, medicine, and current events—are expensive to write. And while every case is different—some nonfiction writers are at least partly supported by media organizations or fellowships—many are utterly dependent on advances from publishers. If legacy publishing craters, or disappears entirely, who will pay for these books? Amazon? Santa?

The nonfiction writer is likely to be a mid-to-late–career professional with a degree in journalism who has years of experience in conducting research, doing interviews, checking facts, and meeting deadlines. Or an academic with advanced degrees and tenure earned for scholarship and a gift for writing. These are writers that publishers can make a bet on, wagering an advance against royalties that the author will deliver an accurate, thorough, well-written book on time. These are writers who can run the traditional publishing gauntlet, putting together a solid, beguiling book proposal that an agent can market to skeptical but dedicated book editors. Such authors also tend to be people with the usual financial obligations of home and family. Writers like this won’t work for nothing.

Nonfiction books also don’t come cheap because their authors must often invest thousands of dollars in travel and research expenses, the cost of spending weeks or even months working in an archive on the other side of the country, or tracking down sources that might be anywhere in the world, or acquiring a small library of books, journal articles, reprints, and copies of private papers. Authors pay for photographs and permissions. It adds up. I’ve got the tax returns to prove it—not to mention a refrigerator-size microfilm reader in my home office that I used every day for three years and that will now be forever retired to the attic.

Expenses and the time it takes to complete a complicated nonfiction book can deplete even a handsome advance to the point where, if you only regarded it as a salary and not as a hope, you’d never do it. Every book is a bet. Most advances don’t earn out and most books sell fewer than 1,000 copies. But editors and publishers, so often and so unfairly accused of caring only for the bottom line, are actually devoted to serious books and are willing to invest the proceeds from their backlists and their bestsellers to publish high-quality nonfiction.

Who will take their place if they go away? Will it be an online goliath that sells everything from computers to hair gel, but would prefer not to have to sell actual printed and bound books? Like everyone, I look to Amazon. But I don’t yet see the publisher of the future. I see Wal-Mart.

William Souder’s biography of Rachel Carson will be published in September by Crown.