Q. Can the Library purchase a multi-user online textbook (etextbook) for my class?
Perhaps. The library can try to obtain a multi-user (or unlimited user) access to a etextbook; however, most of the major textbooks publishers either limit purchase of their etextbooks to older editions and sell the current electronic editions only to individual users with single-user access. Or they simply will not sell their etextbooks to libraries at all. Typically, we are more successful obtaining access to University Press titles and Major Academic Press (like Springer Science, Elsevier, Taylor & Francis, or SAGE for example).
If you want to provide free etextbook access for your students you are encouraged to contact your librarian subject specialist (https://library.sdsu.edu/people/biblist.php) to investigate what options may be available. For Open Access (OA) or Open Educational Resources (OER) you might want to employ in your course please start with the Library’s Open Educational Resources (OER) @ SDSU for Faculty page (https://libguides.sdsu.edu/oer).