65% of students report not purchasing a textbook because of its high price. Source: Fixing the Broken Textbook Market U.S. PIRG Education Fund and the Student PIRGs, January 27, 2014
Open textbooks allow professors to customize and include portions from several sources without requiring purchase of multiple textbooks.
Consider also freely available resources from various digital libraries; just 2 examples (there are many more!):
WashU Libraries is a member of MOBIUS; and MOBIUS is now a member of the Open Textbook Network.