Individual writing of a textbook/book
In a textbook, a scholar accumulates the information they possess. Unlike articles, there's no need to frantically squeeze every paragraph to fit within the required space—who knows, perhaps a particular paragraph will be cited and influence the instructor's Google Scholar rating. Citation rates and the h-index demonstrate how successful a scholar is and how popular their ideas are among colleagues (and, moreover, such a researcher will certainly find their way into various universities). However, ratings and work are far from everything. Publishing textbooks can also be beneficial financially.
The cost of individual writing and publication of a textbook is from 2000$.

