I always thought they were super expensive for just being a piece of rubber -- they're like 5 or 6 dollars in my area for a medium sized one. I bought mine from
www.petedge.com for $1.45.
I put regular peanut butter in there w/o freezing it and Stewie at all of it out in a matter of minutes. Now he just bats it around like a cat & watches it bounce. He loves it.