Now, if you basically don't know or have trouble understanding the material? I wonder to what degree some tutoring and even a fair bit of time are going to make up for years of poor school outcomes (for whatever reason). Some specific strategies are 1.) pretty straightforward--if you can quickly narrow options down, maybe guess and move on--and 2.) won't move the needle a lot.
Want to do well on the SATs?
1. take all the math classes your high school offers
2. pay attention in those classes
3. read a lot of adult-level books (I read tons of scifi)
and you'll do fine without needing any gamesmanship.
Me, I struggled and came pretty close to flunking out.
In my opinion and experience of the results my peers got, these kinds of standardized tests were really pretty good. The tests and studying methods themselves didn't necessarily mimic what you would do in a real job or even a university degree and sure seemed stupid and annoying at the time when you had to do the damned things... But stepping back and thinking about it, for the most part the people who were intelligent and capable of a motivated and disciplined approach to academics and fields that typically require degrees did actually tend to score better than people who were lacking in those things.
Yes there was the occasional very intelligent person who wasn't disciplined or motivated for whatever reason who did poorly. They weren't or wouldn't have been happy or done well in college either though, for the most part. And there were a few uninspiring intellects who got extremely high marks withe the sheer grind, although I think that's an impressive attribute itself and probably very useful for a lot of fields. There certainly were not hordes of Einsteins and Newtons just slipping through the cracks because they didn't test well.
So I don't know. There is this "common wisdom" that tests are terrible, which is an attractive idea. I just don't know if that's really true. Maybe they're actually pretty good for a large proportion of people.
I don't have any good ideas to get away from that.
It's possible our declining academic performance is simply another artifact of rising inequality.
Or what matters most - who is willing to put in the effort.
You already have 6 hours a day in high school. Don't need more time than that. As for money, that's not needed either. Your high school math books will do. There's also the public library, the Kahn Academy, youtube, etc.