“To make matters worse, he may end up choosing an expensive college (I’ve always told him that I would support his choice since I assumed he would choose a path that would lead him into a prosperous future.)”
Now is the time to get completely honest with yourself about just exactly how much money you are ready, willing, and able to pay for your son’s education, and under what conditions. And yes, it is OK for you to set conditions. It is your money. But you need to let your son know what those conditions are so that he can consider all of his options.
Run the Net Price Calculators at the websites of at least one Big State U in your home state, one Big State U that you’ve heard of in some other state, one Place I Dreamed My Kid Would Attend, one Good Art School, one Place I Figured My Kid Could Get Into. Then think long and hard about where the money could come from for any of those. If you can readily pull together $70k each year it is one thing. If you will have to scrape to get to $20k it is another.
With an ACT in that range and an equivalent GPA there are likely to be affordable (or even nearly free) options if he’s not picky about where he studies. Some of those places will have good Art Education programs: http://talk.collegeconfidential.com/financial-aid-scholarships/1678964-links-to-popular-threads-on-scholarships-and-lower-cost-colleges.html#latest