The cost is probubly due to the R&D and marketing along with a huge profit margin becasue if all we are talking about here is releasing ozone into the water all you need are 2 close proximity electrodes (titanium spark plug) for a spark to jump across and a high voltage (4kv) low current (1ma) spark generator like a dog "Fido Shock" fence electrifier. Place the titanium spark plug shielded in a strainer in front of a power-head and voila, one aquarium ozone generator about $20. Because the spark jump is so small yet intense it should both produce good ozone while elimination and possibility of shock to fish, especially since it is shielded.
You could actually install it inside canister filter or sump. All that is needed are the calculations on intensity and exposure which I believe is probably very broad and safe, 1 minute a day should do it zap-zap-zap. Ill have to place this on my DIY list since I have a used Fido Shock.
