Alright, I am doing a hypothetical for you to get an idea as to how to figure out a guesstimate:
Fathers Gross income: 80,000 + Mother's Gross income: 20,000 = 100,000.
Father has 80% of the income while mother has 20%.
Now, what the child support office will more than likely do (they do this in PA) is take into consideration normal expenses (rent/mortgage, utilities, etc.....not cigarettes, vacations, etc) and deduct that from BOTH gross incomes. Let's say the deductions are even (which I am pretty sure they will do simply because if he is paying $1500 a month for rent/mortgage and the average cost in the area is only $600 he would most likely not receive the credit of $1500). Now after these calculations he would most likely be responsible for 80% of the allotted amount to care for a child, let's say it's a thousand just to keep our figures less confusing for now, then he would be responsible for paying you $800 monthly.
Now if you are unemployed, the state would most likely assign you an income in which you should be making which usually is min wage at 40 hrs a week.
Here in PA min wage is $7.15 so annual gross income would be: $14872
Father's Gross income: 80,000+Mother's Gross income: 14,872=94,872
Your portion is approx 15% while ex's is approx 85%.
Again, just a figure to play with, $1000/month is figured for care of child making his responsibility $850/monthly.
Again, they will take out for expenses but you can also push the issue of medical coverage and child care expenses as well.
Best of luck.