Have you ever thought of getting some 150W heat lamps and suspending them all in a row across one side of the room (so that the cham cant get to them) with some climbing stuff underneath? Would this let them go to the warmth when they need it? I mean, Im not sure as ive never heard about this before, but I have a 150W on the beardies big tank and it gets to 131F under the light (I had to move it higher so it is now holding steady at about 100F directly under it with a cool side of the cage and plenty other spots, so no worries about burning themselves.). They get HOT, so Id imagine they would heat one side of the room nicely.
Just a thought.
Mark
EDIT: And if your room is under 25x25, a space heater should be great. We have a strip space heater that we paid about $100 for that heats our entire living room well (30x25')