you can get away with it cheaply enough by just using the 6 dollar one at lowes/home depot
here is a little video on how to make the thermostat work better
and here is some of the bators people have made.
https://www.backyardchickens.com/a/homemade-chicken-incubator its a pretty basic...
there are some good examples of cooler-bators on byc incubator sections, thats how i built my first one and it worked great, i hatched 12/18 my first try.
gl, all you really need is a 60watt bulb, a water heater thermostat, and a container.