Checkout this thread on cage heating:
http://ball-pythons.net/forums/showt...04#post1845904
I buy professionally made cages but their design may help you. Here is a thread that goes over my cages in detail:
http://ball-pythons.net/forums/showt...With-Pictures!
I have used ultrasonic misters in the past and would advise you to stay away. They require weekly maintenance and can really be a hassle. You are much better off getting a warm mist system. I also wouldn't put it inside the cage. You can pipe the mist into the cage or humidify the entire room. Honestly a humidifier is overkill for most ball python setups anyway. There are better methods of regulating humidity.