Money and politics have always been closely related. This was true even in Ancient Rome.
At the time of the Emperor Augustus, a man had to possess property worth 1 million sesterces in order to qualify as a member of the senatorial class. (There was no pretense of populism in Ancient Rome, and no shame about the class system.)
How much money was 1 million sesterces? Well, it is almost impossible to convert the amount into British pounds or American dollars. A Euro conversion would be even more difficult, given the financial disorder caused by the Greek debt crisis over the past several years. (Sorry—I couldn't resist.)
A sesterce, or sestertius, was minted as a small silver coin during the days of the Roman Republic. By the time of the Empire, however, the sesterce had become a large brass coin. (Yes, currency depreciation was an issue even in ancient times.)
An unskilled laborer in Rome earned about 3 sesterces per day. Employers in Ancient Rome couldn't outsource work to India and China. However, unskilled laborers did have to compete with unpaid slave labor.
Moreover, there was little industry in Rome by modern standards. (Some economists, observing the Italian economy today, would say that not much has changed.)
Roman legionaries were paid a fixed annual amount of about 900 sesterces. This was not a lot; but being a legionary was better than being a common laborer—provided an inept imperial legate didn't get you killed in a battle with the Gauls or the Goths.
A Roman legionary had no chance of attaining the Senate, barring an extraordinary change in fortune. Even if he saved every sesterce, a legionary would have to serve 1,111 years in order to earn 1 million sesterces, and thereby qualify for the senatorial class.
Given that the average lifespan in Roman times was about 28 years, this wasn't likely.