Tax dollars do not fund unofficial travel. If an upper level member of government is traveling for work it’s considered official. If they are traveling for their vacation then it’s on their dollar. When I was working for the federal government we were not allowed to travel first or business class on government travel funds; I don’t believe that has changed. A better question would be should they take a private jet or a major airlines. That would be a question of the security of the trip. Government officials should be able to travel as safely as possible when performing their jobs.