One way to save money on guinea pig supplies is to use a litter box. Instead of filling the cage with bedding you have to replace regularly, you can use litter pans in regular toilet spots and reusable bedding such as fleece everywhere else.
Another added bonus to fleece? Your pigs will love it! Having a clean dry cage means you are free to make small pillows and beds for your pigs to lounge around on, without having to worry about them getting filthy in minutes.