Sometimes sign shops are more abundant then is obvious. Check maps.google.com for "sign" near your city. Also check for "plastic". There are plastic stores that sell coroplast.
I recently made my first c&c cage, and I must say, coroplast is worth the effort of getting it. White sheets are very inexpensive, and they can be rolled up in a large wide roll if needed to fit in a small car. The sign/plastic store guys don't usually realize that it can be rolled, but it can. There is another thread documenting the rolling.
As for other options, it depends. How big is your cage? Is it single, multi-level, or have second floor lofts? Is it on the floor or on a table?
You can usually make due with a sheet of plastic, like a shower liner, painters drop cloth, or polyurethane sheeting from the hardware store. This will work pretty good if you are going with cotton+fleece bedding, and
if it is just temporary until you can get your hands on some coroplast. For loose bedding (carefresh, shavings, etc), you really need a solid tray with sides to keep your sanity. A wood box lined with something waterproof as suggested already will work.
