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 that Amazon prices are subject to change at any time and may have increased or decreased since this offer was posted.