[akstrohm]

You could:

Use a shower curtain for the bottom instead of coroplast. You can find them pretty cheaply in stores.

Look for grids at garage sales and on ebay and craigslist.

Sell the pet store cage and use that money to reimburse your mom for the C&C supplies.

Emphasize that C&C cages smell a lot less because they are bigger and that they are easier to clean. Also with C&C cages you can use fleece which is cheaper than disposable bedding.