Warehouse Deals 4 Less via Amazon offers Prime members Avatar: Last Airbender Complete Book 2 Collection on DVD (pictured) or Complete Book 3 Collection on DVD for $11.74 with free shipping. (The Complete Book 1 Collection is also available for pennies more.) Non-members can spend over $35 for free shipping; otherwise, shipping adds $3.98. Each is $1 under our mention from last summer and the best price we've ever seen. (They're a current price low by at least $6.) Book 1 features 20 episodes on six discs, Book 2 has 20 episodes on five discs, and Book 3 has 21 episodes on five discs.
Note that MightySilver via Amazon offers The Legend of Korra: Book One Air on DVD for $12.88 with free shipping for Prime members. That's the lowest total price we could find by $2. (Book Two is on preorder for $14.96.)