https://www.cccoer.org/learn/
"Using OER can provide tremendous cost savings for students as well as impact student success and completion rates.
The cost of textbooks can be a financial burden on students, which not only affects student success but could also delay graduation for students who are taking fewer classes per term because of that cost, further increasing financial costs for students over time. OER provide students with day one access to free course materials, and research reviewed by the Open Education Group shows that most students perform as well or better using OER course materials compared with students using traditional textbooks."

2016 Florida Virtual Campus Student Textbook & Course Materials Survey Chart 1: Impact of Textbook Costs on Students
Why Open Education Matters from Blink Tower on Vimeo.