There are some great free resources online, including some automated prep programs! One of the best is "Number2.com." This is an interactive program. The difficulty level of the questions is adjusted to your ability!
Another great free website for SAT math prep is "SAT Math Pro." This site provides audio-visual explanations to select math problems.
Other free websites worth looking into include: "SAT Exam Prep.com," "I Need a Pencil.com," and "Major Tests.com," These sites provide automated test like questions for all 3 sections of the SAT.
Finally, there are some test prep sites which offer 'limited' free resources. The best of these (by far) is "Perfect800.com." This automated program gives users the opportunity to try out some of their SAT math questions for free! (Over 800 problems are available for a nominal monthly fee).
Remember, to make the most of these resources, you really have to be self-motivated! Moreover, if your scoring requirements are in excess of 50 or 60 additional points, it's unlikely that working with these automated sites will suffice... However, they’re a good starting point!