Help with college books

Hey everyone, I am a single mother of 2 kids. I work full time and I am also trying to better myself by getting a college education part time in the evenings and weekends. Tuition is covered for the most part with financial aid. However books are my responsibility and do not come cheap. I have never done this before but my friend said its worth a try. Any help you would be able to give me towards books I would be forever grateful for and may it be paid forward to you in the future. Thanks in advance.