Your project sounds super badass! I was curious so I did some searching and found some good stuff when I looked for battery powered fog machines, specifically the Wizard Stick! ($23) http://www.amazon.com/American-Science- … rid_pt_0_0
According to the comments this thing works like a spray bottle with a heating element. When you squeeze the trigger it turns the element on and squirts a bit of juice onto it. I’m sure that, with some modifications, this thing will do exactly what you want. If it were my project I would rig up a servo to the stick’s trigger and then use an arduino to turn the servo every 30 seconds to a minute to conserve battery life.
There is also something called a smoke pencil that would be perfect ($34, check the video) http://www.smokepencil.com/
Alternatively, if you are feeling industrious you could totally build this yourself with an electric pump, an electric cigarette lighter, and a spray nozzle. Hmm, I think that I really want to build one of these now!