The original series had several references to money, though not always a specific currency system. Harry Mudd was a trader and con man. The dilithium miners were trying to secure their fortunes. Same with the miners on the planet with the Horta (had to look that up). Quark also had a lot of Federation customers, and I'm sure he didn't take anything on barter.

whomod said: I generally don't like it when people decide to play by the rules against people who don't play by the rules.
It tends to put you immediately at a disadvantage and IMO is a sign of true weakness.
This is true both in politics and on the internet."

Our Friendly Neighborhood Ray-man said: "no, the doctor's right. besides, he has seniority."