The frang was a unit of currency in Takar.
The Takarian bard recited the first verse of the Song of the Sages for free but demanded 3 frangs for the next verse.
The Ferengi stranded on the planet demanded 10 frangs for a copy of the Rules of Acquisition, cheapest binding.
Soon after, they found profits from Ga'nah Province were down to 148 frangs. (VOY: "False Profits")