there is a system in place for dental treatment for teenagers but not kids
however i understand the expense but even putting a few dollars away a week will cover a check up even if its once a year per child, its better than nothing.
having worked in the industry i understand the costs, you can also ask your dentist if he will let you pay off basic treatment such as check ups and when the time comes, things like fissure seals which is preventative work
things like cheese are awesome for kids as it helps to neutralize acid from food etc..

ETA was also going to ask do you have a school dental van in your area??