score:7
The Angus Maddison Project provides the following GDP per capita (in 1990 GK international dollars) estimates for regions within the Roman Empire in the year 1 CE:
Population-weighted average is probably somewhere around 700*. There were around 45.5 million people in the Roman Empire in the year 14 CE.
So 45,500,000 * $700 = $31,850,000,000.
* Note I'm not too concerned with the exact average because these are all imprecise estimates anyway. But you can choose your own number between 600-800 to multiply by the population if you disagree with mine.