You can pick up the shipping heat packs on Ebay. They're not that expensive. Having extras on hand for emergencies is an excellent idea. I use 72 hour heat packs for shipping--the peace of mind is worth the slight extra expense.
(Tip on using 72 hour heat packs--open them the night before you ship, so the pack can age out and spike its temperature before you put it in the box, otherwise it may shoot the temperature up too high, as it takes longer for 72 hour packs to spike than 40 hour packs do).