If you buns are litter trained, you can use a wood pellet litter in the litter box and blankets or towels in the rest of the cage. Wood pellets cost about $4-6 for a 40 pound bag. You might be able to find them at a feed store (as horse bedding) or a hard ware store (as wood stove pellets). Either one is fine as long as they are kiln dried. You could put them in the rest of the cage, and scoop up the wet spots every day and clean the whole cage on a weekly basis.
Food prices vary depending on the food, where you are located, the store and the bag size. Knowing where you are and what food you have/want would help a lot.