I have been doing a fair amount of research into a portable fridge for an vehicle expedition I am planning on doing from Baja to Alaska. The problem lies in the Peltier thermoelectric technology used in the new cheap coolers; they just don’t make really cold temperatures.
To my knowledge there is nothing great in the sub $100 range, but there are excellent efficient cold fridges made for expeditions. These will actually freeze stuff. Unfortunately the cheapest is about $550. They are the ones with the sealed Danfoss compressors. These portable fridges/freezers are marketed by Waeco, ARB, and Engel and are all basically exactly the same products. You can pick which one you think has the better customer support; I can’t say which that is yet. I would probably go with ARB, as they have a very high rep in the 4×4 community. But the Waeco USA site also has a ‘factory reconditioned’ section that is worth keeping an eye on for the right model.
[Review updated with new model links and image. -- cc]