Best SAT Preparation Website (Prep Scholar, Green Test, Khan Academy, Others)?

I am a current junior with a 1330 on the December SAT. I’m aiming for above a 1400 from the March SAT and at least a 1500 in August. I wanted to use Prep Scholar (as they have the +160 point guarentee) over the summer for the August test, and I’m apart of a weekly Compass Prep virtual class for my March SAT (I go to a boarding school, so I don’t have the time to use Prep Scholar). What do you recommend as an amazing, guarenteed results, less than or around $400 prep class? Has anyone tried Prep Scholar and seen significant results or have gotten their money back due to the guarentee?