The ancient world knew no such thing as regular wages or set salaries. Nevertheless, money does not, as they say, grow on trees, and urban and rural dwellers alike required a source of income to be able to provide themselves with the necessities of life. The wealthy landowning portion of the population, which held abundant assets in land (though not necessarily in ready capital) and the richest merchants had few problems in the realm of yearly income. For the vast majority of the ancient population in any society the major source of economic activity was agricultural labor. Nearly the entirety of the population of the Roman world--arguably the largest and best organized economy of antiquity, and certainly in the Mediterranean--could be found working the soil in Italy or their provincial plots, which rapidly were reorganized according to the highly efficient systems of land use the Romans and Italians preferred. Agricultural workers could range throughout the economic spectrum. Most were tenants renting plots or, if they were spectacularly unlucky, unlanded free labor of the sort to which Achilles compares kingship over the dead. These individuals lived by the labor of their hands, and in the case of tenant farmers the left over produce after paying their rents could be sold or, if there was not enough surplus (much small agriculture was hardly above the sustenance level), provided for the family unaided. A relative few owned their own plots, usually a few jugera, either inherited, purchased somehow, gotten as a veteran settlement or (during times of the most horrific civil strife) through proscriptions and other nefarious means. But like the tenant farmers, these individuals lived hard lives. Often they were not far from the sustenance level, and the threat of a bad harvest could ruin a farmer completely. The city was constantly taking in new migrants, being a cesspool of disease to a degree that the birthrate alone was unable to cope with the rate of death to disease--yet grow the city did, mainly due to migration from the rural areas (although not, as archaeology seems to show, at the rate at which our texts suggest, or at least not in the same way). Failed farmers had little choice but to work someone else's fields or move to the city, where opportunity might potentially present itself. Deployed against such financial threats were stockpiles of surplus and what cash could be got for them, and most importantly loans. That crippling debt that Cicero and Sallust mention during the 60s and that broke out again in the civil war targeted the nobiles most dramatically (public life was not cheap), but the majority of debtors could be found in the country. Farmers bought their land often on credit, paid their rent on credit when harvests were bad, traded in livestock and seed on credit when necessary, and if really pressed were forced to buy food on credit or put up their own property.

The city is where the bulk of our meager evidence for Roman wages and labor is found, however. Here no one could rely on the surplus of their own fields for food, and without hourly wages and fixed salaries the inhabitant of the city of Rome earned his pay daily. For a relative, fortunate few this wage was more or less secure. Artisans, shopkeepers, and other skilled tradesmen could rely on the profits of their own shops and workshops. The demand for finished goods and so forth maintained for most skilled workers (most of whom, if our epigraphy is to tell us anything, appear to have been freedmen, likely taught a trade while in bondage) a decent living wage. These individuals, who owned their own modest businesses, could take on additional workers, and might even own a few slaves, were able even to take a few days here and there off work for political activity--P. Clodius called on the shopkeepers to close their shops as a gesture of tribunician strength, secure in the knowledge that the skilled workers could close their shops or leave them in the charge of their slaves and workers. This plebs media, while still generally part of the capite censi, should be clearly distinguished from the mercenarii, day-laborers, who made up the majority of the city's population. The vast majority of inhabitants of the city of Rome were landless, semi-migratory day-workers who wandered through the city seeking work daily. They probably paid their rents daily (so suggests Frier), living without permanent shelter--and perhaps none if they could find no work for the day! With families in tow--and families they did have, since migration alone does not account for the increase in the city's population--they lived on the knife-edge of starvation. Average wages are hard, even impossible, to calculate, but we usually take Cicero's statement that even an unskilled slave could make three denarii a day as our starting point. Likely Cicero is exaggerating heavily--one denarius is probably more realistic--but even if he is, Cherry has shown that even six denarii a day was woefully insufficient to keep a family alive. Rents, though likely daily, were not cheap in the city, and the price of grain was highly flexible, especially in the Republic before Augustus' measures to prevent manipulation of the grain market. The reduced price of grain provided by C. Gracchus and P. Clodius' elimination of any price for the state-subsidized grain whatsoever helped, but the state's allowance consisted of only 5 modii a month, enough for an individual but totally insufficient for his family. Under Augustus the plebs lost their right to state-subsidized grain, and only a relative few were allowed it, with no provisions made to ensure that only the needy were granted access. Grain had to be purchased on the market, and at market prices between food and shelter little more could be afforded. Public largess, no matter how meager for the individual, could be a major blessing, extending a family's budget for several months or allowing them the luxury of a diet beyond bread and porridge. We have a very few indications as to possible wages. At Pompeii we have preserved the average yearly pay of the staff of the duoviri--local apparitores, and therefore skilled workers and something approaching public servants. Scribes, the most important apparitores, made at Pompeii 1200 HS, while the lowest-paid apparitores only made a pathetic 300 HS. Only a handful of positions paid much more than 400 HS at Pompeii, and this is without considering days lost. Even these relatively skilled and important workers were hovering dangerously close to the minimum necessary income--food, by even the most generous estimations, could regularly cost somewhere between 300 and 400 HS. To the ordinary unskilled urban worker, toiling daily at the monumental building projects, in the docks, or perhaps in some artisan's workshop at some menial task, a livable income was hard to grasp. The urban plebs, far from the 19th century evaluation, were not an "idle population," feeding on the largess of the state with no need to work. They worked for a living, providing daily the only economic service most of them had access to: the labor and strength of their own bodies.

EDIT: I should probably also link this, especially since it's quite recent