Some of my editing clients publish through hybrid presses. No skullduggery there; it's a straight-up hybrid. A hybrid press is another way to purchase a publishing services package. Some hybrids are more open than others, and plenty will tell authors that they're meeting a higher standard than Everybody Gets Published. It's true. When you consider how bad a book could be at the moment of submission, it's a good business move to keep the lowest-caliber books out of a hybrid's work flow. If you only write the books, hybrids carry you from a final draft to the for-sale moment. $2,400 is not an unusual number for a hybrid quote.
Here's a good thing to know: if all you write is the book, you're probably going to see a fraction of the sales if you'd written essays, articles, blog posts, Facebook posts, and even long Instagram captions. Or maybe just a great newsletter. Publishing needs authors to write after the sale. Or, you can get lucky and get a contract where you get some help from a marketing department to write some of that stuff.
I don't see any problem in publishing through a hybrid, so long as you understand it's on par with self-publishing done professionally. Belt Publishing, which does great books in traditional agreements, also operates Parafine Press. It's a hybrid. The profits from Parafine help Belt pay its bills on the traditional book deals where the book doesn't earn its way to a profit. This drive for profit is one of the things that hammers down advances. Anne Trubek, who heads up Belt, has a wonderful book out, So You Want to Publish a Book. It's the best $10 you'll ever spend on your career.
Authors have invested in getting their books published since, oh, the 19th century, maybe earlier. There's also a process called subvention, where someone invests in the book besides the press. Subventions are more common in academic presses.
Ever since I sat down in an editor's chair, I've known publishing is a for-profit business. That was clear from that first job in 1981. That publisher closed its doors 90 days after I went to work. The losses just got too steep there. If nobody is earning anything from a book, it's usually not because that was the intention. A vanity publisher is still a publisher, but their gate is as open as your investment makes it.
There's nothing wrong with vanity publishing. When you get honest about what a traditional deal amounts to, it's an advance and maybe a sales force and good promotion, plus somebody else to pay for creating and shipping the books. The traditional press grooms you for another book and attaches its influence and connections to its better-known authors. That's why a traditional deal is prized; some of that is hard for anyone to offer except a traditional press.