How do I get a reduction in child support without change of income?

I have been divorced for 2 years. At the time of the divorce, I held the high paying job and he was a contractor. He said he could not live without a certain amount a month in child support in order to keep the house and allow my kids to go to the same school. I felt guilty, so agreed to a enormous amount of child support. He also gets paid in cash and personal checks in order to hid the funds. Things have changed!
He has remarried adding 4 more people to the household. She does not work. The custody for my kids is split 50/50. I have them 2 days a week and every other weekend and so does he. I pay to feed them and activities when they are with me. He does too, but I do not get any child support from him.
My position at work has not changed, but with the economy change, it is hurting me. Is there any legal way I can get the amount I am paying him reduced to reflect the legal amount that I am obligated to pay, not the "extra" to keep him comfortable?

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You should request a hearing through your local child support agency. Whether or not they will change it I can't guarantee. But you should try. Maybe his income has changed.

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Child support calculations do not usually account for income or expenses not directly related to the biological parents.
If you can show that there has been a significant change in your respective incomes then the CSEA may adjust the amount of support, but generally only if the effective difference in payments will be 10% or more.