FIrst ask yourself if the test prep is necessary. What were PSAT scores? My children had them in 9, 10, and 11 grade. All the scores were within 100 points of each other. We didn’t do any prep. Ivy/Elite schools were never going to be a consideration. Outside of bragging rights, higher scores weren’t necessary.
Remember too, you don’t need to pay for a class for prep. Every library has the test prep books, or you could buy them , or your high school may provide access to Khan Academy or something.