Where can I find a better base for my rat cage?

My rats have been chewing holes in their plastic base to the cage they are in. They have plenty of things to chew on so i just want to get a different base. Most people suggest buying a cage with a metal base but I don't want to buy a completely new and expensive cage. Is there somewhere I can get a metal bin or pan or something to use as a base? And does anyone have any suggestions on something else I might use to fix my problem?