The best advice I could give him is to seek God's will for this important decision. God knows all about him, and God also knows what's best for him. Could anything be better? The Bible says, "As for God, his way is perfect" (Psalm 18:30).
You see, God loves us–and because He loves us, He not only knows what is best for us, but He wants us to have it. Encourage your son to pray about this decision and to seek God's leading. The Bible says, "Trust in the Lord with all your heart ... and he will make your paths straight" (Proverbs 3:5-6).
You don't indicate if your son is a Christian–if not, I pray he will make his commitment to Christ now. Yes, college is an important decision–but his decision for Christ is even more important, because it affects both his eternal destiny and his life right now. He will face many pressures in college, and I don't believe a young person can fully resist them without Christ in their heart.
As a footnote, I also would encourage your son to consider a Christian college. Yes, private schools can be expensive but most have generous financial aid packages. But wherever he goes, urge him to put Christ first in his life. This is only the first of several major decisions he will be making, and God wants to help him.