BuyDig offers the Xit Hardhsell Backpack for DJI Phantom 3, model no. XTHBPDJI3, for $94.95. Coupon code "TAKEOFF35" drops it to $59.95. With free shipping, that's the lowest total price we could find by $35. It features carbon fiber construction, adjustable shoulder straps, and will hold the DJI Phantom 3 drone and accessories.
Also available is the Xit Hardhsell Backpack for DJI Phantom 4, model no. XTHBPDJI4, for $64.95 via the above coupon. That's the lowest total price we could find by $85. It has similar features to the DJI Phantom 3 case.