Have you thought about MN State Mankato? They have a good math department and he can transfer elsewhere with good rec letters from there if he doesn't like it.
Put yourself in my shoes. It's great that my kid got some college credit in high school but MN is not a great place to raise a family anymore nor is it safe or .... "Quality of life" isn't really a thing like it was.
And you see this from all sort of people here. Lots of people who grew up here are sick of it and want to leave or are in process of leaving.
For where I'm not sure.