Using Harvard as an example for a family of 3, US citizens living in Massachusetts, 1 in college, $0 assets, all income from wages/salary:
https://college.harvard.edu/financial-aid/net-price-calculator
Income ($) Net Price ($) Net price / Income (%)
0 4600 infinity
10000 4600 46.0
15000 4600 30.1
20000 4600 23.0
25000 4600 18.4
50000 4600 9.2
65000 4600 7.1 (highest maximum aid income)
100000 9600 9.6
150000 19600 13.1
200000 45000 22.5
250000 66350 26.6
255000 69600 27.3 (lowest no aid income)
300000 69600 23.2
350000 69600 19.9
400000 69600 17.4
The maximum ratio of net price / income is found at income = $0. The minimum ratio is found around the middle income level when below to super-high income level (the ratio gets down to 7.1% at a local minimum at $65,000; it eventually falls to that level at $983,481).