Everywhere I have cruised was within reach of the U.S. Coast Guard so the helicopter will be at no charge. Amazing how far they will go. A co-worker was half way between San Diego and Honolulu on the Amsterdam when his appendix burst. U.S. Coast Guard sent TWO helicopters for him......just in case one crashed they told him, AND a refueling aircraft. All, free of charge to him. Even flew him back to San Francisco, 30 miles from where he lived so he could be treated by his Doctor.
His rescue and video of it are mentioned in this report......showing how frequently the Coast Guard not only does medivacs, but delivers blood and medicines to cruise ships, all for free. But you do have to be somewhere close to a U.S. Coast Guard facility, so this would not work on a European cruise, but certainly on a Caribbean, Mexican, Alaskan or Hawaiian cruise.
http://abcnews.go.com/WNT/video/air-drop-delivers-blood-cruise-passenger-15443765