I've been thinking about taking one of those small fridges that might hold 2 or 3 gallon jugs and building a ghetto foam enclosure around it. Of course I'd leave the back of the fridge open to vent heat, but I'm betting the fridge is more than capable of keeping a 5 gallon carboy around 50 degrees since it can damn near freeze a couple cases of beer when I ask it to. The only cost would be some foam board and some time since I already have a temp controller.