Child Care Issues IL

I am a divorced father of two children. I make a fairly decent living and have never been late on my child support in the four years that we have been divorced. In the orders it says I have to pay 50% of any child care expenses. The problem I have is that the ex is on a set schedule but when she needs to save for a trip or wants to work her whole weekend the sitter fees go up double what I pay. For example by court order I pay $1,000 a month for two kids plus around $88.00 a week for day care expenses. I have the right to take the kids when she works but....I have to work and work more to just support myself with these fees. Is there a cap for child care so I am not always broke even with a decent salary??