I agree with Larry about the space heater idea. I think a space heater is also less expensive than enough CHEs to heat 3 cages.
That set up looks way too top heavy and cumbersome to clean. I'm astonished that they used only factory connectors and not zip ties to hold it all together. If you stack them 3 or 4 high (to keep one off the floor) you might have to anchor it to the wall.
I wouldn' recommend stacking more than 3 high, maybe look into a ferret nation set up. They are great for multi-hedgie homes