What I did was this:
Supplies:
1. A styrofoam cooler (can be found at walmart)
2. A fish tank water heater (make sure the heater is fully submersible)
3. 2 bricks
4. a mesh screen (don't know what to call it.) The screening doesn't have to be like the one in the picture, its purpose will be explained later, but im sure you know where im going with it.
Instructions:
1. Place one brick inside the cooler against the wall. Place the other brick against the opposite wall. (face down, not standing up high.)
2. Place the aquarium heater in the middle of the coolers floor (between the bricks.)
3. Run the wire up the side, and make a little indentation on the rim of the cooler so that when the lid is closed, it seals nicely around the cord.
4. Cut the metal screen to fit snuggly against the walls and resting on top of the bricks. (you most likely will scrape up the inside of the cooler, but its ok.)
5. Fill with water and turn the heater on.
Warning: make sure the heater is fully submerged in water before turning it on. And make sure that it stays fully submerged.
6. Add your thermometer and adjust the heater until you get the temp you need to be constant.
Overall, I made this in less than half an hour, and hatched all but 3 of the 19 eggs in the batch.
Was very reliable temp and humidity wise.
-Brandon