Help for the guinea pig cage I'm making?

I'm making a C&C guinea pig cage, (cubes and coroplast), but the coroplast is way to expensive, but it's the bottom of the cage, without it i cant build it. Coroplast is usually what signs are made out of. Its basically a laminated piece of cardboard. Is there anything else i can use for the bottom of the cage that's not a fabric or cardboard? If you have any ideas, please let me know where i can find it please and thank you!