there is no need for a dry climate grow house for your cacti.

i grow cacti down here in florida and trust me its plenty humid here and rains pretty much every day durring summer. you just have to plan accordingly. pot your girls up in the most well draining thing you can think of. I use cacti soil, perlite, and coarse sand as my mix. i go really heavy on the perlite and sand too.

if you get the proper drainage daily rain wont hurt your cacti. as a trade off the faster drying/more airy growing medium has to be watered more often durring non rain months to maintain max growth.

youre wanting to spend too much money when you could just change their growing medium and keep them outside until you get near your first freeze, if it freezes there. if youre up north stop watering around the end of october, and bring inside in november for the winter.

as my buddy ringworm would say, "these are not desert cacti, give them water and theyll flourish."

youre just gonna have to do a little hit and miss experiments.

goodluck.