The shipping method you are referring to is called Delta Dash. Call your local Delta airlines and ask for this service. The price I paid was $85.
Is it heated? The aircraft is controlled but time spent on the ground will be at the temperature of both the departure and destination locations. I have had a couple of reptiles shipped by this method without incident. On a few occasions both parties have agreed to wait for better weather. Your reptile will be down loaded on the ground with all baggage and packages in that aircraft at its destination. I have waited up to 45 minutes after arrival time at the Delta Dash desk and watched the operation from the window. Its fast, but the cold or heat could have a direct effect on you reptile depending on time of year and temperature plus the length of time on the ground.
My recommendation is to first know the temperatures at both locations for that particular day of shipment. Second is to use a slightly larger box with thin sheets of Styrofoam to line the inside. You can use sheared newspaper to cushion the snake inside the box. And put the snake in a snake bag (cotton pillow case). Make sure the person receiving understands to be there on time at the airport this is critical. Oh! Do not feed your snake prior to shipment and make sure your snake has pooped its last meal before his flight (important).
Hope this has helped you.