For this year, you might want to check and see if Champion Force exists in your area. It's a lot cheaper than All Star (I think here it's $9/week), and with a RO-BHS, you could probably make their level 5, which would have you working on, mostly, level 1 and 2 stunting skills. All competitions are in-state except for Nationals (and teams would have earned bids at the winter State competition, so the only way you'd go to Nationals coming in this year is if they needed a substitute), but since it's officially 2 seasons/yr, coming in mid-year is possible. If they don't have a level 5 or won't allow mid-year tryouts, as a high school student, you'd automatically be on level 4, which is the equivalent of level 1 all star with some stunting variations.
The average skill level is a lot lower and less intense than All Star-or, here in TN, than school cheer which is dominated by folks who did All Star since age 3-4, but it would give you some cheer experience.