Utah Open Textbook project has created a calculator that will help you assess what the costs/savings are for your institution when comparing use of commercially available textbooks against that of open textbooks.
Allowing the user to specify a range of variables (e.g. length of time textbooks are normally used, cost of the textbook and number of students who need to use the textbook) the tool calculates savings by also taking into account the cost of educators remixing the content according to their own needs and how much time/money it will cost for educators to revisit the textbook and make adjustments every year for the specified period.
Results are shown as follows:
“With your current textbook, it costs $120000 to provide a textbook for each student (at a cost of $11.43 per student). If you adopt an open textbook, over those same 7 years you’ll invest $4500 in your teachers, another $39194 on printing. Taking these costs together, open textbooks will cost your school or district $3.73 per student (32.66% the cost of your current textbook).
The Bottom Line: With open textbooks you’ll save $72106 over the 7 years.”
(Source: http://openedgroup.org/calculator/index.html using default settings of 1500 students, textbook at cost of $80 and a 7-year cycle for replacing the textbook you currently use)