A terrarium can be made from an old aquarium. I got two 5 gallon aquariums that I use for hospital cages for my budgies, but I could set one up on end, fit a tray or pan of gravel in the bottom and set a few pots of orchids inside, leaving what used to be the top, but is now the front, open for air to circulate. that would help hold moisture around the plants. A cool mist vaporizer might do the job for you, too.