At the SAT Information & Registration link these resources are available for free or low-cost:
SAT Question of the Day ~ Answer a different SAT practice question every day for free.
SAT Practice Test ~ See how you score and get detailed answer explanations to help you better understand where you need to improve for free.
SAT Online Course ~ 18 interactive lessons, official practice tests, sample essays, auto essay scoring, personalized score reports and more - subscription.
SAT Study Guide 2nd Edition ~ 10 official practice tests or the study guides for SAT Subject Tests featuring previously administered tests.