the thing i have found about SAT calsses is there is a HUGE difference between the good ones and the crappy ones, and that is reflected in the price. I took one at my high school that cost like 100 bucks or so and it was ok, but didnt really raise my score that much. The Kaplan ones that supposedly raise your score 200 points however cost over a grand.
Now, i beleve that as long as you practice, you dont need to take a course. I got the "10 real SATs" book, and simply doing the math problems over and over boosted my score a lot. The math itself isnt hard, you just need to be able to do the calculations quickly and accurately. For verbal, my mom bought me a SAT vocabulary book and made me learn 10 words a day all summer long. Sure enough, many of those words showed up on the test. If ya wanna know, i went from 620math, 630 verbal to 730 math and 700 verbal. Good enough to get into MIT