“Dual Enrollment doesn’t exist” doesn’t sound right; is there no university nearby (doesn’t sound like it)? It may be called something else (PSEO is another name for it) but before you’re sure DE doesnt exist, check with your guidance counselor. If you go through your high school, you should be able to take your morning classes at university or community college, and your afternoon classes + clubs at the high school.
This would be especially important if you’ve exhausted all your high school’s math offerings.
High income + no savings is a bad combination for college - you may get into Top 25 universities and not be able to afford them.
You’ll need to look into colleges that offer major merit. Beside USC (California), there’s USC (Carolina), UAlabama, Northeastern, Tulane, Emory, WashU; NYU has been known to love math prodigies (AIME-level) as well as Northwestern, not sure how HarveyMudd or Scripps would treat you (I think Scripps has merit aid) but the consortium garantees you never run out of math classes. Wellesley might be a possibility since they have merit aid and cross registration with MIT.
https://www.math.hmc.edu/program/department/facts/