Where can I look for free or cheap textbooks for my classes?
UCSD SPACES has free textbook rentals. You should sign up for their mailing list so you will know when the fall application is posted.
online 
Occasionally on Tor
Ucsd free and for sale FB groups sometimes have some
won’t work if you are using ucsd wifi (they blocked it) but will work with a vpn or a hotspot or someone else’s wifi
If you use UCSD WiFi without a VPN you’re crazy
Then I think there are a lot of crazy people here 