Thank you for your question.
When it comes to the many flights conducted by DFO and the conservation and environmental protection people, I don't have the cost information at hand either. No doubt, there's a significant difference in cost between the use of sonobuoys and the use of aircraft surveillance. Each has its pros and cons.
Aircraft surveillance can identify the exact location of a whale, so it's possible to better define the area that should be closed off to fishers. Sonobuoys can detect a whale at a farther distance, but they don't tell us where the whale is in relation to the buoy, so that's a drawback.
In short, flights do cost considerably more, but they can detect right whales and identify their location with much greater precision.