AP Macro/Microeconomics + E&M self study

Hello everyone! So I’m a junior in high school, and I’m taking 5 AP courses (US History, Physics 1, Computer Science A, Language/Composition, Statistics). Last year, as a sophomore, I took 4 tests, BC Calculus, European History, Psychology, and Physics C- Mechanics. I performed well on all of the tests, and I want to go into a math/science field. I’m trying to take as many AP tests as I can, and because of that, I’ve decided to try to self study the AP Economics courses, and AP Physics C- E&M. I believe that these 3 classes, on top of the 5 I’m already taking, are well within my ability. But my problem is I don’t know what the best study resources are. For the economics courses, I’ve been taking the Khan Academy Macro/micro economics courses, and they seem great, but don’t seem to provide the in-depth knowledge required to take the AP tests. For E&M, it has come to my attention that the calculus becomes more challenging, with line and surface integrals. Because of this, I’ve been studying multivariable calculus, and familiarizing myself with the maths necessary.

But to those of you who have self studied these courses, what are the best online sources? Is Khan Academy a good place to start? Part of the reason I’m taking AP Physics 1 is so that I can get good help from my physics teacher. My family doesn’t have a lot of money to burn, so Princeton Review books aren’t really in the question. So I ask for all of your help and opinions.

TBH, Khan Academy is not the best source for certain AP classes. The best online source would be the College Board Website, where they have past FRQ’s posted. But if I were you I would go to the local library and get the prep books, of which Barron’s books are typically the best for AP Prep.