If you look at the raw numbers, only 3 people died in the boston bombings. But if you look at the economic costs,
- The entire boston transit system was shut down for security reasons, disrupting the entire city
- Large numbers of people did not go to work the next day, costing hundreds of millions in lost productivity
- An enormous manhunt ensued, at the cost of over 300 million
- Entire parts of the city were shut down, preventing them from going to work
- 10s of millions in costs to the victims
- Tens of thousands of hours of additional work for public employees
- Billions in lost productivity nationwide as people focused on the media saga
All this cost the terrorists only $200 in explosives. In your words, billions of dollars in economic damage "is just minor nuisance".