I've been starting to collect data to document the economic impact of Applied Discrete Structures.  In a class using our text, the cost to a student ranges from $0, if  he/she uses the pdf, to $30 a hard copy of purchased.   A rough estimate of the percentage students that buy a hard copy is 15%.   Prior to using our text at UMass Lowell, we used a text that cost $160 new, and around $120 used.   So a very conservative estimate of the impact on student costs would be $120 times the number of students enrolled in discrete math classes using our book.  Here are the estimated student savings, also with very conservative estimates for enrollments starting Fall 2011 through the Spring 2013 semester:

UMass Lowell:   300 students have saved a collective $36,000

Other Colleges:   75  students have saved a collective $9,000

That's $45,000 that students have saved in the first couple of years that the book has been available.   We're hoping that with increased exposure on open source textbook websites, we can dramatically increase the impact outside of UMass Lowell.

So far we are listed on the following sites: