Both of these can be had for free at your local library. And to be pedantic, you don't even need a desk to study you can do it on a park table or the sidewalk. If someone doesn't have access to a desk (they're homeless?) or an internet connection, I doubt they're even taking the SAT.

I was homeless my final year of highschool, and basically homeless the year before. I took the SAT, but it was hard to figure out how. Even harder to bring myself to study rather than work.