If you don't want to have to wire your own DIY lamp, I use a clam lamp or any lamp below are pictures for examples.
Below I have gathered materials that you prolly have sitting around your house. 10''x10'' box. Tape, (not in pictures but kabab skewers to support basket/ made of hardware cloth.) a foam lid. Foil. A 15 w bulb.
Below cut a hole in the box for the lamp to go through...
put down foil, on the floor of the box. Then fish the lamp through and on top of the foil 15 w bulb. Hang the basket 4 '' from the top, I would rest it on poked through the box, wooden kabob skewers, and you can tape it also. Tape edges well so chicks cannot slip through the egdes when they hatch.
I have a foam lid on this, but you can have a solid box lid, and on top a glass lid from a pic frame (Just cut a hole in the box. This glass lid is what you would use to lift (not the foam) to turn eggs. (The foam lid is taped down.) Poke holes in lower part of incubator, and upper part of incubator to create "still air effect." and oxygen draw.
Below is a pic of it warming up.
If the egg wire basket tray is too warm add on top of the wire and under the eggs a loosely woven cloth, leaving the edges of the wire more open for air flow.