If I am assessing an applicant and see a degree from UCLA on his resume, I think "OK-good, next item." If I see a degree from Princeton, I know this applicant is a superstar. A Princeton grad will have been challenged to really think, competitively and collaboratively, with some of the finest minds in the world. Even average grades at Princeton mean quite a lot. And that Princeton name will stay with him throughout his entire life, whatever he does and wherever he goes, opening doors.
I'm not saying such intellectual development isn't possible at UCLA -- just that it isn't a given. IF your son is ambitious and aggressive about pursuing opportunities and standing out from the crowd. (Note that it's a really big crowd there...) Bottom line, if he's got the type of personality that will make him a "big fish" in any sized pond, then UCLA is a financially prudent move.
But if he's one to swim along with the other fish and just quietly do extremely well, then a smaller, more nurturing school might be much better for him, and he'd emerge from Princeton with a world-class education and a 'Wow!' credential.