Ozone can for sure be VERY dangerous and you really do have to know what you're getting into when you use it. I personally emply ozone and love it, but I only use a 50mg unit and run it at only ~35mg. A 300 would be way overkill for your tank which is smaller than my own 65g. If you really do want to go down the ozone route, research a LOT and impliment slowly. Back the unit off if you ever see signs of stress in livestock (especially corals).
As for power consumption though, Ozonizers only use a few watts of electricity, so little you probably won't notice it on an electric bill