Here's one option, go down to your local Home Depot and pick up a Sunbeam Wine Chiller for around $120.00. Then order 1 lb. of Premier Media beads from climmax.com for $30.00 which will maintain five cubic feet at 65-70% humidity, depending on what you order for beads. This particular wine cooler is 5 cubic feet so 1 lb. of beads works out perfectly. Then scrounge up a small cooling fan from an old computer. I bought a timer at walmart for $8. I hooked the cooling fan to the timer, mounted the cooling fan to the bottom rack of the wine cooler. The fan comes on twice a day and circulates the air in the cooler.
The added bonus of using a wine cooler, depending on where you live in the country, is that you can actually turn it on for a little while if it gets too warm inside. We don't want those tobacco beetles hatching.
Granted this a bit more expensive than your basic igloo cooler, but you also get a few more options IMHO (racks to store your boxes on, glass door to look check humidity without having to open it, etc.) .
Tim