What's going to be your source of carbonated water? Will it be store bought bottles/cans like Amano first used? Isn't that going to be comparatively more expensive?
I havent decided yet - using a simple pressurized system you can produce carbonated water for about $.04 per 2 liters. That or wholesale canisters.
That being said, during this process te importance isn't cost, but to determine thresholds and other methods of Co2 delivery - a reverse engineering if you will.