Best way to reduce lighting/heating costs is to put heat lights on a proportional thermostat which will reduce or increase power to the lights according to temperature.
Effective cage design would be one that prevents heat escape. Glass and screen are bad for heat escape but screen doors or glass doors on a otherwise solid wood or other solid material cage help hold heat in. Screen tops really leave heat escape fast so best to cover most of the screen top (make sure there is no fire risk if hot laps are setting ontop of a cage, instead of mounted inside, when covering the top screens).
In the summer, block your AC vents to the room your reptiles are in, if at all possible, to help keep it form getting too cold (also, AC units suck up more power than anything else...better to close all the blinds during the day to prevent the house heating up due to the sun shinning through the windows).
Unfortunately the more energy efficient bulbs tend to work against herp keepers who want heat energy as well as light energy from bulbs. Compact fluorescent bulbs produce plenty of light energy but little heat so are useless as a basking bulb...leaving us with halogen or regular light bulbs to provide heat for our scalely friends. Since you do live in a very warm area most of the year, you could move your dragons into more screen cages and let them have access to the same direct sunlight your iguana has. Natural sunlight will suffice for UVB and heat, as long as care is taking to ensure your dragons don't get too hot (ie provide shaded areas for your dragons to get out of the sun if they are too hot).
-----
PHLdyPayne
