Sometimes the best playthings are those that didn't cost a thing.
When I finish a jar of peanut butter, I put the top back on and hand it to one of the dogs. My mastiff (God rest his soul, he died nearly 10 years ago) loved to figure out how to take the top off the jar (which was plastic) and he could be kept busy for hours trying to get every last bit of peanut butter out.
I have also purchased real bones and once the marrow has been eaten out of them, I've stuffed them with peanut butter.
During teething, you can place the bones in the freezer so whatever stuffing you used is frozen. This calms the dog's gums while he tries to get every last morsel out of the middle.