Unless you live in an excessively dry area mistings should be sufficient. Also, for a species such as a Ball Python the humidity is only important in the animals burrow(s) or hide box(es).
For BP's I've used terra cotta flower pots or bases with holes chipped in them. These flower posts are designed to "breathe" and are an excellent way to provide humid burrows for species like BP's. It's the breathability that allows them to soak up water and have it evaporate out slowly.
If you mist under a terra cotta pot once a day and the humidity is not high enough you could then try soaking the pot in water overnight. Perhaps have several pots. That way you can have some soaking and others that have been recently introduced into the cage. By having several you could also offer multiple hides to the animal. Some warm and wet, some cool and dry, and others inbetween.
Otherwise, I like the ultrasonic humidifiers made by Sunbeam and others. Very easy to run either aquarium tubing or PVC pipe from the exaughst port and into the terrarium. Make sure your use distilled or reverse osmosis water in these systems.