I don't think it's necessary to pay money for a prep course to do well on the SAT or ACT. It may not even be helpful.
Do You REALLY Believe in Expensive Test-Prep Courses?
But it is necessary to read a lot to do well on standardized tests, so it helps to have access to good libraries and good reading instruction.
I've wondered myself whether the college admission scale is still tipped in the direction of wealthier, more academically average students rather than poorer, smarter students.
Do Colleges Actually Prefer to Admit Wealthy Students?
Good luck in your applications.