textbooks.com, ebay.com, or you can google textbook sites and see what you find. Compare prices and make sure to check the feedback and the seller’s rating. I had it once where the book never came (money refunded)…annoying to have to buy it twice, late in the semester.
It depends on the class. Public speaking-you have to speak in front of everyone so taking with a friend might not help. Something like economics or math you can take on your own because, well, they are single-person classes. No real group projects or assignments. I guess it depends on the science teacher. Most science classes I would try to take with a friend- labs, reports, projects… it all depends on the teacher.
I would avoid some political or history classes (try online). That way you dont have to deal with teachers’ biases- anti-israel which mean anti-jewish according to them…