Amazon has 76.5-oz Gatorade Thirst Quencher Powder (Frost Glacier Freeze) for $8.29 when you check out via subscribe & save ($1.18 extra savings will be applied at checkout). Shipping is free.
Note, you may cancel your Subscribe & Save subscription any time after your order ships. Select the later date from the "First Delivery On" menu to get traditional S&S checkout instead of adding to your cart.