Many household things are suitable as toys for small animals. Pet shops sell a variety of expensive toys but this doesnt have to be expensive.
Toilet roll tubes: Stuff them with hay for a fun toy. they love pulling the hay out of them.
Carpet rolls- most carpet shops will give the inner rolls free of charge. These are ideal and safe for guinea pigs. They are the same as 'chubes' but are free!
A hay rack- these provide lots of fun for guinea pigs living in a large run. Stuff with hay and lift of the ground for them to pull the hay out.
Cardboard boxes with a hole in them- you can stiff these with hay to provide fun but also they love hiding in them and destroying them!
Old towels, kitchen cloths- these provide hiding fun, snuggly beds and lots of fun!
Paper bags- stuff with hay and hide veg and treats inside for lots of fun.
Bricks- old bricks provide great excersing toys. Climbing on the them and standing them on edge with veg and treats on provide great excerise for piggies.
Teracotta plant pots- large ones of these are great hiding places. You can use smaller ones stood upside down. Stick a carrot in the drain hole and piggie loves to get this. Its great excerise for them