The article states "At an estimated present-day price of approximately $10 per watt of laser power, building and operating Breakthrough Starshot’s 100-gigawatt

The article states "At an estimated present-day price of approximately $10 per watt of laser power, building and operating Breakthrough Starshot’s 100-gigawatt array today could cost as much as $1 trillion." but goes on to say that the price is plummeting quickly, and so may be affordable in relatively short order.