This is not a question we can really answer in a firm way.
For example, the coin that was quite literally the gold standard of currency from the fourth century to the fall of Constantinople in 1453 was the solidus. When it was first coined (it was later debased several times), there were 72 solidi per pound of gold. Right now, gold is valued at $16,310.37 per pound, so a fourth-century solidus would be worth 226.53 USD.
This, however, tells us very little about the actual contemporary value of the solidus, so we look at some example prices. To earn a seat on the town council in a North African city required 300 solidi, and the wealthiest Roman senators had annual incomes in excess of 2000 lbs of gold (more than 144,000 solidi). Unfortunately, these are also not very helpful measures, and do not give us definite answers, but rough approximations. We do not, after all, have the same sort of government structure.
The figures I have given here come from