First, A Brief Primer On Book Publishing Options
Traditional publishers: They accept manuscripts for publication that meet their standards (whatever they may be), provide authors with an advance against royalties (an advance against the author's take of sales), and provide all the work necessary to publish books. And there's a lot. The author takes no financial risk but receives a small percentage of the cover price of each book, since the traditional publisher needs to make back its investment...and presumably more. Many traditionally published books don't sell enough to cover the authors' advances.
Self-publishing: Authors publish their books themselves, doing...and paying for...all the work necessary to do so. And there's a lot. Over the years, I've read that it's not unusual for self-published writers to pay around $10,000 to publish a book of a quality to compete with traditional books. And then they may sink a lot more money into marketing. The authors are taking all the financial risk but receive all the money their books make. It's not unusual for self-published authors to not make enough money on book sales to cover their investments.
Hybrid publishers: Hybrid publishers are supposed to be somewhere between traditional publishers and self-publishing. They provide some of the work necessary to publish books but authors pay for a portion of it. I'm seeing figures of around $8,000 to $9,000, and while that does include distribution, which self-published writers struggle with, it often doesn't include developmental editing and marketing. Both can cost a lot. Authors are sharing the financial risk with the hybrid publisher but receive a bigger percentage of each book sold than traditionally published authors do.
Looking Further Into Hybrid Publishing
Jane Friedman takes a deep plunge into hybrid publishing with IMHO: A Nuanced Look at Hybrid Publishers at The Hot Sheet. Read it carefully. Among other things, she talks about the percentage of authors publishing with She Writes Press, a well-known and reputable hybrid, who earn back their investment. I found it sobering.
A few years ago, I attended a women's writers group. A few women had books coming out with a hybrid publisher. A couple of them said they were going that route, because they were older writers and didn't want to spend the years it can take to find a traditional publisher. Yeah, that was sobering, too.
These days, we think of traditional publishing as being the gold standard. That's where the quality is. But I wonder if a couple from now we won't be thinking in terms of quality, but social class. People with the means to do so, will publish rapidly with self-publishing or hybrid publishing. Poor writes will congregate with the traditional publishers because they don't have to put any money up front with them.