Amazon has the KONG Air Dog Balls (3-Pack) for only $3.39 and free shipping for Prime Members when purchasing them as an Add-On Item.
If you are not already a Prime Member you can join with a 30-day free trial of Prime, as a student with Prime Student, or as part of Amazon Family.
Please note: Amazon prices are subject to change at any time and may have increased or decreased since this offer was posted.