Do it your self for free nest boxes
First you will need
a large drill bitt, 3 screws, a drill, a saw, a five gallon bucket, and some wood.
next you will need to cut your wood to fight the bucket you want it to cover 1/3 of the opening of the bucket.
then you will screw the bucket down to...
its only hard to read the red liquid thermometer. a digital or even a blue liquid thermometer would solve that problem very easily.
and definitely go with a red bulb.