something else to consider Johnny, how wide is your water bowl? I mean, how much surface area? That could help with the humidity if you can't switch to aspen or some other substrate.
And also on the substrate, you only need to spot clean, and clean the tank about once a month or so. I don't really see how it would cost too much. We can get 4 cubic feet of aspen for 10$ here, and that will last probably a year!