In-state public school has a lower sticker price, but have less non-loan need-based aid so students have to come up with a high percentage of the sticker price. The top private non-profit schools have higher sticker price, but provide a lot more non-loan need-based aid, so students have to pay a much lower percentage of the cost. At Princeton, for example, the average debt at graduation is only $5k.
http://www.nytimes.com/2011/09/29/nyregion/seton-hall-univer...
This is definitely a trend in private education pricing as sticker shock is a real problem for students considering private schools and the privates compete for the same students the publics do.
This assumes no need-based financial aid, and doesn't touch on housing, which is assumed to be 10-13k these days regardless of public or private.
Just about everything in undergraduate education is well established enough that you'll learn the same material anywhere. You'll find variation in the material covered (e.g. Catullus versus Ovid), but it's mostly window dressing on the same core concepts. By the time you get to a graduate level, it becomes important to pick the right institution to ensure that your personal area of research was well represented, but paying extra for undergrad is simply a waste of money.
How are you supposed to afford spending that much on a single child's schooling and still have enough to afford the rest of the family, retirement, insurance, mortgage payments, etc? Sure they could have planned better and saved for 20 years but the reality is that a very small percentage of people do that.