Cheer Coach of 12 years here...
When we did make them ourselves we would use foam poster board. It was light and easy to work with. Sometimes we would paint them with stencils but the most fun was using stencils for letters and then filling the letters in with lots of glitter. The foam board was at places like Pat Catans and JoAnn's.
Then, we got tired of the signs wearing out so quickly and not being able to use them during the rain. So, we went to a professional sign place and had them made on a VERY light/not heavy board material that was corrugated (sp?) and waterproof. They used a vinyl lettering on both sides. I believe for us to get about 9 signs front and back cost us $150 I think.
They have lasted at least 8 years so far....with lots of use.
I understand about the parents being tapped out. We got our boosters to help with things like this because they were not personal items for the girls. They are considered school property.
Good luck.........