Luckily, sparkling water is easy to make at home and countertop carbonators have become pretty cheap ... SodaStream Terra ($100) included. That $100 gets you the sparkling water maker plus one CO2 ...
and SodaStream tank among other low cost parts. The most expensive component was a CO2 sensor which cost $230. The rig uses an Arduino for feedback and control. With a total BOM cost of $350 ...