Update: 'Temporarily out of stock. Order now and we'll deliver when available.' Look for Amazon AU in the 'Other Sellers' section.
Medium size is the cheapest at $8.99. I believe this is the cheapest price it has been on Amazon.
Small size is also $ 10.49.
"Mentally stimulating toy, offering enrichment by helping satisfy dogs’ instinctual needs
KONG classic red rubber formula for average chewers
Unpredictable bounce for games of fetch
Great for stuffing with KONG Easy Treat, Snacks or Ziggies
Made in the USA. Globally Sourced Materials." From Amazon Description