Student loans. And maybe some scholarships.
Oldersisters idea about colleges coming down in prices is a great one, but who knows if it is realistic.
Gusser makes a good point about staff making paycuts. This could be possible at some schools with particularly high pay rates, but I know at my college the professors salaries were hardly something to write home about... so I think that's a good suggestion, but I don't know if it is relevant to all colleges and universities.