you can buy them for 20$ or you can make one yourself.
To make one you need:
one Styrofoam bait bucket with lid,
One night light with long cord
tin foil
duck tape
a zip lock bag
a thermometer
first you make a hole in the side of the bucket and place in your night light (high watt bulb). Then you line the entire thing in tinfoil. Then cut a square out of the lid big enough to see threw. The place the zip lock bag over to make a window and duck tape. Then place in the thermometer and try it out. You want the temp to be about 99*
kind of like this one but without the wire mesh , the bowl or the fan (only need these if your are hatching chickens lol.)