Great question and one that we are facing right now.
We were lucky enough to put money away for both my son and daughter early on for there college education. What I didn't expect though is that what we put away will only cover about half of each year's total.
A few things come to mind....
First of all don't be afraid of the college's "list price". My son's private DIII school took $4,000 right off the top for alumni and diocese scholarships. He was then offered an additional $8,000 in academic money.
From what I have found out, colleges tend to give more academic money to applicants whose SAT scores are above the school's average. If your son enrolls, then he will in effect be raising the school's average SAT score. Which is what the school wants. It looks good in print and they now can attract a "smarter" student and some would argue that the college can now justify raising tuition, etc.
Lastly, just think now you won't have to pay the price for that private high school and can now shift those funds to collge.
Good Luck....You're not alone!