It’s a tough call, but if Caltech is your son’s dream school and was admitted, he is not doubt of the special stock that can handle and appreciate Caltech’s curriculum and focus. Depending on your son’s areas of interest and career goals, CalTech is one of the schools were you can very reasonably expect very comfortable earnings. As others suggested a combination of “parent grant” + debt might be the best approach.
Take a hard look at the “cheap” in-state schools, the quality of the undergraduate body can be pretty appalling, especially at very large schools, and extra-especially to a guy who was accepted to Caltech. I’m the product of a cheap state school and now humbly work for Techers 