Consider filling in some of the gaps by using library resources, such as e-books and articles.
Licensed e-books, online magazines & journals, streaming media, and other online resources available through the Seattle Central College Library subscriptions are not considered Open Educational Resources. These resources are restricted to SCC students, faculty and staff, and they are already-licensed materials that do not allow for customization and re-use or redistribution the same way as OERs. Although library online resources are not "open", they are considered "alternative educational resources" (AER) that you can take advantage of and make available at no cost to your students. Library resources are also sometimes referred to as LER, which stands for licensed/library educational resources.
This 5:26 minute video explores how library materials can be an important component in solving the problem of high textbook prices.
This webinar from 2013, hosted by the Open Education Consortium, explores how libraries and librarians are involved in supporting open courses, OER, and helping develop open policies.
Interactive open educational resources: A guide to finding, choosing, and using what's out there to transform college teaching by 
Open by 
The World Is Open: how Web technology is revolutionizing education by 
Massively Open by 
Open Access by