We're starting year 3 after completing yrs. 1&2 in the grammar level and we've used our public library system for nearly all of the books. In MN at least, our public system accesses the universities and seminaries as well as all of the public libraries within the state. Occasionally we've purchased books for TOG because they would be used for several weeks or because we loved the book so much. Per year we've spent less than $100 on books for TOG, which has made this curriculum very affordable for us.