Cheaper ideas? Well, most of the ones I've been looking at seem to work on water vapor- and there are clips out there showing people experimenting with just that sooo...

I'd say use a 'vaporizor' humidifier- because it's actually steam and will rise higher than cold water humidifiers and ultrasonic fountain transducers (they make a nice low fog tho!). The real trick would be on how to 'train' the vapor and direct it to desired location without losing moisture along the way (anytime steam contacts a surface- like the wall of a pipe- it's going to condense back to liquid- especially at the relative low temp we're talking about here) and also control its velocity. I also think using fans on the steam is going to knock a lot of the moisture out of the air as it passes through the fan blades...

So just off hand I'd say get a quality home vaporizor humidifier ( or commercial if you have the dough), set it below your 'fire pit' area- figure a way to distribute it with as little surface area as possible, and light it with colored lights. I was going to say - use LEDs to light it, but it may be a better idea to use incandescent because of the added heat they will give to the air and may promote air movement without the use of fans. In fact it may help to put the vaporizor in a box that is heated with heat lamps or similar to really get the air flowing. OBVIOUSLY we're talking about water and electricity here... don't be a fool- do it right- use a GFI amongst other precautions.

I think the added heat would also cut down on residual moisture problems as well.

At least your monsters won't have to worry about pesky dry skin irritation...