It would be interesting to see if they used different light wavelengths to excite the water molecules if they could make the process even more efficient. If you can match the wavelength to the water electrons energy level during the electrolysys they may get better yeild for less energy input.
As for the price of bottled water, I need to point out that enough clean fresh water falls from the sky each day around the world to meet mankinds current needs. Besides, most of the planet is covered in water. If we stop wasteing fresh water, there would be plenty for everyone.