Well this is pretty easy so here's what I got:
10 gallon fish aquarium
styrofoam cut to fit aquarium as a lid
large pickle jar(pickles should be eaten of course)

submersible heater
thermometer
deli cups/vermiculite/hole punch/labels
Basically you fill the pickle jar with water, put in the heater and place the whole thing off to one side of the aquarium, then plug in the heater. Whatever type of thermometer you use it should read the temps inside the incubator not inside the deli cups, so place it accordingly. Hole punch 5 or 6 holes into the rim of each deli , fill them 1/3 full of vermiculite and add 3 tbsp of warm water and mix it well. Then you just add your eggs, label them for the date laid and the parental genetics and put the syrofoam lid on, weighted if it doesn't fit tight and viola! easy incubator. If you want to be really cheap skip the heater and place the incubator somewhere that keeps a constant temp. Just remember that you will need that jar filled with water anyways so that the humidity doesn't drop. Hope this helps you out!

Julie