How do you self-study for an AP?

College Board has this thing called a CED (Course and Exam Description). In this document, you can find everything that is going to be tested on the Exam. I think that if you look at the CED and use it to guide your self-study, then you should be fine for the exam itself.

I would recommend contacting your counselor or your AP coordinator for your school. They will provide more accurate logistics on the price, but generally, I think it's around $70-$100.

Here's a link providing you with some answers on the other parts of your question: https://blog.collegevine.com/?s=%22self-study%22

omg i clicked the wrong tab

I found a website called fiveable.com that is helpful to study for the exams. You still have to pay for the AP if you want to take it, no matter how you study. I find that listening to calming music helps me stay in the "study zone" if you know what I mean, lol. But other than that, use Khan Academy too and it really helps!