I don’t think OP means he can’t EVER leave the farm. He’s 16. He hasn’t graduated yet.
Library books are free. Most courses with a teacher costs money. They’re having financial problems. If the son wants to learn, he can find a way. It’s not a requirement to take SAT prep classes. And once school starts back, he should be able to discuss with his guidance counselor what kind of classes he needs to take to better prepare him.
OP said In their edit that med school is expensive- that’s why i said they’re not responsible for paying for it.
I know this will be downvoted too, but you can’t always depend on your parents to help you with stuff like this. Especially if they are struggling to put food on the table.