Another option to consider would be U. of Idaho. It’s part of the WUE exchange. It only has 6900 students, is ABET-accredited, and has D1 sports, should that be appealing to your son. WUE tuition is $9300, and I wouldn’t be surprised if your son got a better deal.
Montana State: This one’s a bit larger with about 14,000 students and a gorgeous area for those who love the outdoors. About $8500 for WUE tuition.