There's a math error there. You divided $100 billion by 12 to get person-years, which would imply a cost of $12 per year. $100 billion / 12 months = $8.3 bill

There's a math error there. You divided $100 billion by 12 to get person-years, which would imply a cost of $12 per year. $100 billion / 12 months = $8.3 billion per month / $100 per person per month = 83 million people so $100 billion per year could give 83 million people $100 per month.