Shipping Frozen Food - Need Advice

Hi!

My sister lives in Mississippi and keeps nagging me to send her frozen deep dish pizzas from Chicago. I have explored some of the issues:
- Ordering and shipping pizza from her favorite vendor is quite heavy in service fees.
- Favorite vendor sells frozen pizzas at their restaurants at retail cost. Ok, I don't mind spending $18 for a pizza I would otherwise spend $18.
- I have a source for the styrofoam cooler and the dry ice. I'm planning to to put the cooler in a box to further insulate it.
- From reading websites, I believe Next Day delivery is required ... but could I get away with 2nd day?
- What I have not been able to determine is how much dry ice is needed to safely transport her food whether it is Next day or (hopefully) 2nd day.

I plan to ship at least two pizzas weighing probably 5 pounds with a diameter around 10 inches. This part is guestimating but I believe I am in the ballpark.

If you can advise to my specific circumstances, terrific. If there are rules of thumb, then please advise. Or tell me where to go to find this information.

Thanks in advance.

Regards,
Cathy2