DIY guinea pig toy: Paper bag of hay
Have any spare paper bags lying around? For quick piggy entertainment fold the edges back, stuff with a handful or two of hay and lay them sideways in your cavy's cage.
To encourage foraging you can mix up different types of hay if you have them on hand. After successfully claiming the sole vacancy for herself, Poof was spotted gleefully digging through 2nd cut timothy, bluegrass, and orchard grass hay.
When the bag becomes too dirty to use it can be composted or emptied out and recycled. Since some pigs enjoy hiding and pooping inside a bag can become soiled rather quickly. For example, Belka and Peaches insist on using the hay filled hideaways as their personal toilet. Paper bags rarely last for more than an hour or two when they are around!