Easy enough.
Supplies: 1 styrofoam cooler 1 lightbulb with socket 1 25w lightbulb 1 roll aluminum foil 1 small bowl 1 piece of wire construction mesh. 1 thermometer 1 small battery powered fan. (can be found in camping supply aisles of most major department stores)
First: Line all sides, including top of cooler, with aluminum foil. Place several holes the size of a standard pencil around the sides. (I shove a pen through and put about 10 holes) Then: Cut a hole in the top just big enough to fit the bulb through. You want the entire bulb inside the incubator, with the plastic socket touching the styrofoam, or the bulb will melt the foam. Glue or tape the socket in place so it doesn't fall on your eggs.
Measure the construction wire against the bottom of the cooler - turn the cooler upside down and trace the bottom on the wire. You want the wire to be 4 inches bigger all the way around.
Cut 3" squares out of the corners of the wire so you can fold the sides down as legs. Bend the wire until you have a small wire box.
Put the bowl into the bottom of the cooler, fill with water. Put the wire box over the bowl.
Place fan and thermometer on the wire. Place eggs on the wire. Make sure you don't run out of water. If the temp is too cold, cover some of the ventilation holes with tape.
Good luck.