Well . . . just to be clear, Obama is the leader of our country. He is not just a member of royalty that hs been stripped of all actual authority. So it's not really a fair comparison.
Don't be pathetic, there is more to it than authority. Besides, how much can Obama do without approval from congress? Does that make him mostly useless too?
Why does Obama get the white house to live in? Why do US tax payers pay for that? Why do US tax payers pay for a whole fleet of presidential aircraft and other vehicles? Why does he need an army of people supporting him? Why doesn't he just stay at home and work in a small corner office of some generic building? That's about all the UK prime minister gets. Why all the show and "pompous" around Obama? Don't you have internet in the US and conference calls in the US?
Lemme give you a hint, Obama fulfils the same role as a royal does besides having authority to launch a "nucular" strike.
So let that sink in and realize that sending Obama on a trip might cost a fortune, but it serves a purpose. Same thing with the royals. Their paid travels are government business. Makes sense the government picks up the tab.
No idea how much it all costs.
Well then how can you make a comparison? Just the cost of the presidential air fleet easily eats up $200 million a year (low estimate). Then add the maintenance cost on the buildings that Obama uses, extra travel expenses for foreign trips, protection costs, the costs of his advisors, household staff, cigar moisturizers, the amount of money that ex presidents still cost the US tax payers and the cost of the first family including the dog. If you add all the costs I honestly doubt that you'll end up with a figure that's far below a billion dollars.
BTW $80 million sounds like a lot, but it's only that much because the US economy is in the gutter. The people in the UK "only" paid 40 million pounds. Most of that is for maintaining government property and travel expenses for government business trips. She gets something like 7 million (pounds) to actually spend herself and even that is mostly used to pay for official expenses of the household.