Fans can very inefficiently cool below ambient - The process of evaporation. When I lived with my folks, my room would be a nice 88 to 90 degrees in the summer. I hooked up 3 12 volt Computer fans to a piece of plywood and aimed them down at the water - the tank cooled down to 4 degrees below room temperature. (84ish) to save my fish when I wasn't around to do cool water changes. The water level would drop quite a bit... almost half an inch a day on a 44 gallon corner tank.
*edit* just saw 50-60*f... Yeah, no way with this method. *foot in mouth*
Ever heard of these:
Piezoelectric coolers - Relatively efficient, but you'd need a big one!!! Nice thing is that they are silent.
There are some portable fridges that use this - You might be able to cannibalize one for 60 bucks? I have one at my desk at work made by mobicool.