Let's assume that you would need 1000 machines to have as much throughput as 4000 people.
WAG, but I'd wager that each of those machines would cost $500k.
That means 100 million in immediate outlays. WAG 2: fuel/electricity/maintenance is $200/month, and you need a team of 20 engineers to watch over them at $10k/engineer/month. So recurring costs come to $400k.
Which brings us to: 100M/1.3M = 77 months, or between 6 and 7 years.
That, however, doesn't take into account the opportunity cost of the initial $100,000,000 outlay. That brings it up to around a decade.
So, a decade to break even.
WAG, but I'd wager that each of those machines would cost $500k.
That means 100 million in immediate outlays. WAG 2: fuel/electricity/maintenance is $200/month, and you need a team of 20 engineers to watch over them at $10k/engineer/month. So recurring costs come to $400k.
Which brings us to: 100M/1.3M = 77 months, or between 6 and 7 years.
That, however, doesn't take into account the opportunity cost of the initial $100,000,000 outlay. That brings it up to around a decade.
So, a decade to break even.