The Federation Credits referenced in TNG "The Price" were being used in a negotiation with a non-Federation world, and were not being used by Federation citizens within the Federation. It is likely that Federation Credits are something that the UFP uses when it conducts deals with foreign entities, but within its own economy, money is not utilized in the same fashion.
Quark was also not a member of the Federation.
There's a distinction: Money is used quite widely within the Star Trek universe. It is just that the Federation does not use it within its own domestic affairs.
Nog said "Currency-based economy" when referring to the Federation though. That doesn't mean that Federation doesn't have some kind of monetary system in place. There were plenty of reference in DS9 to Starfleet personnel having some kind of payment for Quark (Mentions of O'Brien and Bashier's bar tab). Beverly purchased a bolt of cloth from Far Point Station and having it charged up to the ship.
Janeway mentions the price doubling on a meditation lamp when the Vulcan seller found out that Tuvok was Starfleet.
The Bank of Bolias if referenced in DS9.
There was also a cut scene from First Contact which Picard refers to having some Earth Money.
I could see each planet in the Federation having it's own currency with Federation Credits having a value against each type of credit.