The ongoing search and rescue effort for the missing Titan submersible with five people on board, involving a huge response from American, Canadian and French authorities, is vast in scale, including both the U.S. Navy and the Coast Guard.

The expense for such an endeavor is likely to be equally great, and it is unclear whether taxpayers in the countries involved, ultimately, will be required to pay it. The passengers aboard the submersible paid $250,000 each for the experience of diving to the Titanic.

"These people paid a lot of money to do something extraordinarily risky and hard to recover from,” said Chris Boyer, the executive director of the National Association for Search and Rescue, a nonprofit that focuses on wilderness rescues. The rescue mission, he said, would "probably cost millions.”