https://sport.woot.com/offers/penn-championship-tennis-balls-12-cans-36-balls-1 12-Pack 3-Count Penn Championship Regular Duty Felt Pressurized Tennis Balls (36 Total Balls) for $17.99. Shipping is free for Amazon Prime Members (must login with your Amazon account and select a shipping address in order for Woot to apply free shipping) or is otherwise $6 per order.