This is true, you can build one with no warranty and factoring shipping for about $60-$70, given your time and that we guarantee the fan for 2 years, $80 is not a bad price, you also need a USB A-A cable, a clamp and some plastic welding adhesive. The most a fan can drop the temp is about 3 degrees F and this is regardless of fan size. A fan works by dissipating the insulating blanket of water vapor over the tank to encourage more evaporation. If the tank is closed in by a canopy or the room is very humid the effect is far less. The only way to further increase evaporation is to dehumidify the room or increase the surface area at the top of the tank by more turbulence. Unless the fan is so strong as to create surface turbulence, a bigger or more fans will not have any real effect. I don't know how big your tank is, but in general you will use one fan per 4ft of length and 2ft of width.