As I understand it, fundraising trips are supposed to be paid for with campaign funds, not taxpayer money. Whether this ever happens, I have my doubts. But when the president travels on other than official business, we taxpayers are not supposed to be billed.
On the other hand, if the president goes somewhere on official business, and just happens to squeeze in a political event, we taxpayers are paying for the entire trip.
Well, sorta true.
He is required to pay commercial rates for himself and family. But requiring him to pay the full bill would be insane.