You can also look into University of Illinois (UI) campuses. They are not overly costly (ex. UIUC charges just over $50k/year for out-of-state) and have decent CS programs. Admission to them may not be a sure bet, but if your son really works on the essays, he should have a good shot.
I believe the student body is moderately diverse as well (double check me on this though).
Also, this is a little off-topic, but don’t give up on scholarships just because your son’s academics are the best. There are plenty of scholarships awarded for things outside academia (ex. community service, innovation/ideas for start-up, sports, etc). Checkout GoMerry for such scholarships.