Financial aid is only a percentage of income so by not working, you lose one whole income in order to gain a percentage of the cost of attending. It might depend on particulars, such as the pay level for the job, the financial aid policies of the school and so on.
If your salary is $70k and you quite two years in advance of your kid attending, and stay unemployed for 4 years, you would lose $560k. Tuition, room and board of $70k times 4 is $280k. Oversimplified but just taking a stab at an example.