For Computer Science, at What Point is it Advisable to Consider Cost or Prestige?

That seems to be most common with students who are not (at least currently) ready for college. Even less selective colleges that admit almost anyone are still college, and students who are not ready for college are not likely to do well (although some come back years later with more maturity and motivation to succeed as non-traditional students).

But that is not specific to prestige colleges.