A quantity of silver or gold went for far more than they currently trade on the world market at, since we've long abandoned the bimetallic currency system. But wealth had much more intrinsic value in ancient times. It's very difficult to make a comparison between ancient and modern economies.
But going by the statement in the Old Testament that a denarius would pay a labourer for an entire day (8 hours) of work, we can work out a rough equivalency. Using US minimum wage ($7.25/hour in some States) we can figure that a coin containing 4.5 grams of pure silver equal to 16 sesterces in the time of Augustus was roughly equivalent to about 58 USD today. That works out to about $3.62 USD per sesterce.
One hundred denarii (each being 4 sesterces) would make up a trading unit called a mina. Sixty minas would be a Roman talent of 6,000 denarii and would be worth 24,000 sesterces. This was an immense sum of money to an individual, in a time when a legionary serving in the army would earn 900 sesterces per year.
To be considered truly rich, you were probably a member of the equestrian order, worth about 400,000 sesterces (almost 17 talents) or a Senator with a minimal wealth requirement of 1,000,000 sesterces. But there's rich, and then there's filthy rich. This included the likes of Marcus Licinius Crassus and his 170 million sesterces (7,100 talents) who paid off the debts of Caesar who owed 20 million sesterces (830 talents) in 61 BCE, as well as Pompey the Great who paid 3.5 million sesterces (145 talents) for his mansion in Rome.
But it was all peanuts on the Empire scale, for in the public Roman Treasury at the death of Augustus held 4,000 silver talents, or about 100 million sesterces. In addition, to his personal fortune of 150 million sesterces, one-third of which went to Livia and the rest to Tiberius. Seems like a lot, but it was really a trifling amount for an Empire the size of which the Romans possessed, and reflects how much Augustus spent on public works and Games and conquest. The Imperial revenue would vary, but it has been estimated that it earned somewhere between 400 million to over a billion sesterces a year, all of which would be spent on public works, government administration, imperial expenses, bread and circuses for the people, and most of all, the army.
His successor Tiberius would pursue a very different agenda, and be despised for holding nearly no Games at all during the whole of his reign, and followed a policy of diplomacy and consolidation rather than military; the three Legions lost in Germany were never replaced. The result? After more than twenty years of rule in the Treasury was some 2.7 billion sesterces (100,000 talents); the most the Roman Empire would ever have until matched by Antoninus Pius during the prosperity of the second century.
A colossal sum, to be sure, but one which paled in comparison to the riches accumulated by other rulers. Such as the silver reserves of the Chinese Wang Mang Emperor of 23 CE, who possessed 160,000 silver talents. Or the 200,000 silver talents seized from the treasuries of Darius II by Alexander the Great at Susa, Ecbatana, and Persepolis.