I want to add to Woody's excellent advice. Not only come with prices of items, but also stress that a good percentage of your supplies are used up and need to be replaced each year. Personally I would ask the principal how one is supposed to have a quality program at 50 cents a kid, and ask what they expect could be bought for that 50 cents.Remind the principal that art is usually make and take and that parents are anxious to see a variety of projects to see what their child has learned. If the principal turns out to be not sympathetic, as if he/she knows any resources for you, i.e. PTA, Education organizations, etc. Then ask if he/she could help you organize an art supply drive from parents and the community. As these suggestions might make the principal uncomfortable, perhaps that would encourage him/her to find more money for you.