Right. Replace regular classes with AP classes wherever possible -- and if it's not possible, you can still get the book and self-study. Some high schools will cover the cost of AP tests, but even if they don't, they're much less expensive than college courses.

When I was in high school, AP Psych was considered the easiest of the tests, so I self-studied for it in 9th grade and took the test. (Even though they prohibited high school freshmen from taking AP classes. All I had to do was get my parents to ask the school to let me take it.)

Also, if you/your parents have the money for it, it's never too early to take the SAT -- you can take it more than once and only send your highest score. (Some colleges will let you send in your highest score for each subtest if you took it more than once, but I don't think that's universal.)

SAT-IIs (do they still have those?) are usually hard -- but there are exceptions. My high school let me take up to three SAT-IIs in one day, with, I think, no added cost past the first, so I signed up for the English one, didn't study one bit, and got a fairly high score on it. (I also signed up for the history one and bombed miserably, as well as the Latin one that I was actually there for, so I think this is specific to English. It was mostly basic grammar and reading comprehension IIRC, so if you know how punctuation works, you'll be fine unless they've changed it.)