How much are "cens" in FMA worth? Is there some sort of canon answer to this, or can something at least be inferred from the manga / either anime series?
Working off of some manga / Brotherhood details, we can reach some sort of approximation. I am not sure if there are any details in any of the guidebooks to give a clearer answer and so am only working off what I've seen in the series itself.
Consequently, the value of a single "cenz" doesn't seem to be much. Given that this is a Japanese manga, the most reasonably assumption would be that "cenz" is approximately equal to the Japanese yen in terms of value and/or worth.