For large numbers of copies, the per - unit costs for POD are higher than for press printing. (indiebooklauncher.com)
Some subsidy publishers require an author to purchase a large number of copies of the book to cover the costs of its initial publication. (authorhouse.com)
Some subsidy publishers take on part of the cost of producing the book, but the author is required to make a significant financial investment in one or more areas (for example, purchasing a large number of copies of the book) to cover the company's costs. (kathyide.com)