Fleece bedding is good, be sure to have an absorbent layer under the fleece too. Puppy pads with fleece on top would work, but I'd use something more reusable. Cotton towels, or "uhaul blankets"(shredded compressed denim moving blankets that cover furniture etc, not the quilted ones). Not sure if you'd have the exact blankets there, but probably something similar.
You can always order grids online, depending on shipping costs that might be too expensive. Also sheets of linoleum would work for the cage too.
With four pigs make sure they are all same sexed, and that your cage meets the minimum requirements. Also prepare for having to house them seperatly. They might not get along, and you may have to have more then one cage.