Hit the Dollar Stores....it will inspire you.
Plastic Bugs & Critters
Large plastic bracelets
Barrel of Monkeys
*Eye everything for potential choking hazzards. Some people use Mardi Gras necklaces....I don't because I'm afraid if they chew the string they'll choke on the beads & I've read that the glitter paint they use on them can come off and be a possible hazzard.
For cheap, already have items.... milk rings, but snip them first before placing them in the cage. I use a multitude of plastic bottle caps...milk, water, soda. I put goodies in them and hide them. They are washable if you choose or toss 'em in the trash and replace.
Plastic toothbrush covers, again from the dollar store. You'll see one (blue) in one of my above photos....I hide goodies in them and they love to forage!