One thing that has helped me is a source called NAIRE.
It is a warehouse type of place that donates things to schools and not for profit groups. There is one in Galesburg, Illinois. I'm not sure if it's a national entity or not. The school pays a membership of around $500 a year. Everyone at school orders what they want. We may or may not get anything. If we do get something all the school pays is freight. I have gotten thousands of dollars worth of really high quality equipment and supplies. The only catch is that sometimes the quantities are a little overwhelming at times. I got 5000 styrofoam meat trays once. I also got a themal copier one time. Our school doesn't have a lot of money but the moral support is there from the administrators. I was at a school several years ago where there was plenty of money but no respect. I guess if I had to choose which I prefer it would have to be respect. That being said, I still don't know how any thinking person could expect you to teach with such a low budget. Maybe having the community become aware of the quality of your program would help. I started a Fine Arts Festival about eight years ago so that the parents could see what we do. The administrators and school board looked good in the eyes of the community. I gained a little more support every year. Realistically though, I couldn't do it without the bulk supplies that I get from NAIRE. If you are interested I will try to find out more about them and send it to you.