OP said in (or was in) foster care. That should get you independent status for FAFSA, so you should get pretty good financial aid.
If you have a school or two in mind, you might contact them with your back story and ask them for suggestions. They might recommend you not graduate early and take some electives, or take a gap year (especially if you are young and would graduate at 16). You might also find a mentor at the school who would help you with applications.
Have you looked at Questbridge? Posse? They have arrangements with private schools to support the students they accept into their programs, both financially and academically.