What would you do in this situation?

So it was my last day of middle school today, (my middle school is 7-9). Several weeks ago someone mistook my socials textbook for their own and took it. Of course, they haven't handed it in and it's costing me 81 dollars to pay for a thirty year old stolen textbook. My mom says not to pay it, if they cared that much they would have gotten me to pay by now, but I find that morally wrong. However, she refuses to pay it and I only have thirty dollars, and I recently quit my job. What would you do in my situation?? Thnx <3