He was not equating total military expenses, he was equating ordinary soldier's pay. That should be fairly apples-to-apples. The top charioteer, over his care

He was not equating total military expenses, he was equating ordinary soldier's pay. That should be fairly apples-to-apples. The top charioteer, over his career, earned enough to cover all ordinary soldier's pay for 1/5th a year. Using the figure above of 600,000 ordinary soldiers in Rome's army, that equates to 120,000 soldier-years of pay. It's reasonable to treat that number as somewhat of a constant over the last 2000 years. Now, I am a little skeptical that a US soldier makes $125,000 / year. The pay rates I can find online range from $25,000 / year for a newly enlisted soldier to $90,000 / year for an E-9 soldier with 40 years experience. That produces a lifetime earnings for our charioteer of $3-11 billion, depending on what the average pay for a soldier actually comes out to.