You might try this:
http://www.amazon.com/Kyjen-PP01056-...1300318&sr=8-1
Basically your dog pulls stuffed squirrels out of a tree stump - and chews on them. It's cheap - and replacement squirrels are available. Several of my co-workers have them & report success. My (large) kitten adores hers (I have to spice it up with catnip). You can add dog treats to spike interest.