I make soda using snow cone concentrate. 4oz of this, plus 5 pounds (!!) of sugar and water will make a gallon of syrup, which makes 6 gallons of soda. Most cost effective that I've found.

https://www.amazon.com/dp/B071SK4JXM

More cost savings, if you buy direct

I might try this during 2F, maybe 1/4 teaspoon of the concentrate per 16oz bottle of kombucha.