I installed this fan a couple of years ago. I think I paid about $12 at Fry's Electronics. It doesn't move quite as much air as the original Airstream fan; but it is silent with no vibration. Note: Some reviews on this site say they are noisy, but these are installed in desktop PCs at ear level, probably about 24-36 inches from the user. In our Airstream, I can't hear it at all, and my wife says she can tell it's running but can barely hear it at night when nothing else is running (like one of the FantasticFans). I originally thought about adding a second fan, but after using it for some time now, I think it wouldn't make any difference in cooling and would just add to the battery load.
Enermax Magma UCMA12 Case fan
The little battery fan for the inside of the refrigerator is available at WalMart. Can't remember, but I think it was about $15. It has a ball bearing motor that is silent and allows the two D-cell batteries to last about a month. It doesn't seem to move much air, but it really makes a difference. Evidently, a little circulation is better than none at all, as it evens out the temperature throughout the refrigerator compartment. No more frozen lettuce under the cooling coils or hot drinks in the door. Although, the frozen water bottles have also helped alot.
The infrared thermometer gun from Harbor Freight really helped troubleshoot this problem (about $30 on sale). You can immediately read one or two degree temperature differences on surfaces. Also, use it on the tires.