Do you already have the heating element? How big of an incubator are you making? I am planning to make a cabinet-style incubator. Mine will have a reptile thermostat to regulate the heat. The heat will be provided by a ceramic heat emitter. The thermostat and ceramic heat emitter cost $51 on amazon.com. The only other thing I need is a small desk fan to circulate the air.
I have used a ceramic heater and straight wire the fan and let it run all the time and
then put the thremostat in line with the heating element they work great you can use a
waffer thermostat or go to home depot and get a thermostat that goes in a hot water heater
they work well also i have used both they only cost around 9 or 10 dollars