Do we have any information on how much, in denarii, the average inhabitant of the Roman Empire during the Principate could have lived off? What would an "average income" have been?
Due to the complexity of the Roman fiscal and monetary policy, it is impossible to just give one answer. In 301 CE, for example, the Edict of Maximum Prices by Diocletian set the costs of various goods and services. A general laborer would receive around 7625 denarii while an average soldier would make around 15,000 denarii. To put those numbers into perspective, a half liter of good Celtic beer cost four denarii while the same amount of Egyptian beer was around two.