Remember, the President has a very nice life style (jets at his command, servants, chefs, etc.), and has zero expenses.
I'm guessing that's not part of your job description. ;-)
Actually, they do have to pay for some things and the servants, chefs, etc. are partially for the executive mansion itself, other employees who work there, upkeep, dignitary visits, dinners and lots of other things. It’s not just a private family residence, it is also a large office complex, diplomatic headquarters, communications center, military facility, press mélange, museum, government compound and so much more.