These three have some common traits but the differences are important.
Small press
This is anything but the Big Five. There are a few bigger independent presses such as Bloomsbury and a lot of much smaller ones, many of them operating online and out of someone’s back bedroom. These do not have huge budgets and will often not do a lot of marketing, so much of this is left to the author. Note, though, that all authors have to contribute to marketing and it’s rare for those who don’t to have much success.
The very small presses rarely pay advances and even when they do these are small. However, many of them offer much more generous royalties, such as 50% of net sales. Be aware though that sales may not be as high as with more established publishers.
A small press will not ask for contributions to the costs.
They risk the amount of time and money they have to spend on setting up titles, editing, cover design, book design, proof reading, distribution, marketing and sending your books to the legal deposit libraries.
Hybrid
You pay anything from a reasonable amount to an extortionate amount to have your book prepared for publication, published and distributed with a minimum amount of marketing. You may like to compare what they’re charging with what freelancers ask for these services and even consider which ones you can supply yourself. Their main saving grace is that you get a sizable portion of the profits on your books. A reasonable hybrid publisher will leave the rights with you.
Vanity
They charge a lot of money, take your rights, and do very little to promote your work.
Buying in services
There are a few companies and a lot of freelancers who offer services for self-publishers. These include:
- Editing (three stages?)
- Proof reading
- Book design
- Cover design
Freelancers can be found on https://reedsy.com and https://www.fiverr.com/
You can mix and match and find the team that suits you if you use free-lancers.
Even if you use a company that offers all of these services in-house, they differ from vanity and hybrid publishers in that all of the rights stay with you.
Two important considerations
Do you have your own ISBNs? Some companies will offer them to you and even if you publish with Amazon KDP you may use their ISBNs. However, a series of ISBNs distinguishes you as a publisher.
More crucially do they take your rights? Clearly a small press does, but they are swapping those rights for the risk they take on the services they provide for your book. A hybrid publisher probably will and a vanity publisher most certainly will.
Web sites offering services and freelancers won’t.