Do you have central air? I had that in my old house and there's a way to add a "sponge/filter" to some systems. It was cylindrical and the air movement caused it to spin and put moisture in the air. It can be a pain as you have to keep it clean or replace it. You also have to make sure it's kept damp (I think there was a reservoir in mine, but not 100% sure now). It can also be a little noisy.
Having said that, it was fairly inexpensive if I recall and went into a small cutout the HVAC company made in the main air duct coming off the main fan for the system. You can use with heat or AC (I live in CT).
I feel your struggles and suffer from dryer weather in the winter as well here and have to work harder to make sure the reptiles are all taken care of.
I had to add a misting system for my Rhacos, but everyone else does okay, with the occasional mist when in shed. I am sure you thought of a misting system and it's complexity and/or cost is prohibitive given the number of animals you have or type of enclosures.
Good luck and keep us posted. I am sure others suffer from the same problem.