How hard or selective are the "Pre College Programs/Summer Programs" of some top colleges?

Like Columbia, UC Berkeley, etc.

I attended Brown University two summers ago. One of my professors outright mentioned how much the school makes from us students. A lot of schools want money from rich kids wanting to live at Ivy League for a while. Last year I was accepted to summer sessions at Yale and Stanford despite less than stellar GPA. Went to Stanford; awesome experience. I’m not sure how hard it is to get financial aid though.

@starrydog Could you be more specific regarding the programs you attended? Different programs may have different admissions standards. Thanks!