I'm preparing for my son to start daycare, and this is the cheapest I've found these lunchbags for. The matching backpacks are on sale as well for $25 (was $39.95).
This other site has them just slightly more expensive, but with more choices on design:
http://www.shopnaturally.com.au/skip-hop-insulated-lunch-bag…
The Skip Hop ZOO LUNCHIES make lunchtime fun time! Sized just right for little kids, or a mum and bub on-the-go. These soft bags have a roomy compartment that holds sandwiches, snacks, drinks and more. An insulated, wipe clean interior keep food and drinks cold. The inside mesh pocket holds lunch money, an ipecpack or utensils.
ZOO LUNCHIES coordinate with the ZOO BACK PACK, the clip-on handle securely attaches the lunchie to the back pack.
Suitable for ages 3+
BPA-Free, Phthalate-Free, PVC Free
Zoo Lunchie measures: 19.1 x 22.9 x 8.3cms
Lunchie available as Dog, Mouse, Monkey or Penguin
THESE ARE FREAKIN AWESOME!!!!
(they are $$$ though considering the size of them, the other site you linked has the lunch bags at about $20 and if you get the school bag at the same time, they cost about $10, making the combo $30)