Does your son plan to major in CS at University of Washington? If so, he must be admitted directly to the major and only about 17% of the spots are given to international students (representing only about 4% of international applicants). That may put the University of Washington into the “reach” category, too. And UW does not have a reputation for providing much aid.
If he chooses a math major, it could still be a match. I think about 40% of international applicants are admitted to other majors, representing about 15-16% of the total student body.