Pay-to-Publish companies can have an array of contracts and services. They all require money from the writer to print the book, but they often do some marketing, retain rights to the book, and take a percentage of proceeds. They may give the writer a few complimentary copies and sell books to the writer at a discount. In some cases, you pay at the front end to be published and marketed, and you pay again to get copies of your book.
Print-On-Demand companies are pay-to-publish companies who are set up to do very small runs of a book. This means that the initial total cost can be much lower, but the price per book is much higher. This usually means that the selling price of the book needs to be much higher to cover the printing cost.
My research for this project will yield a self-publisher comparison chart that I’m looking forward to sharing on the site.