I think you're missing the point.
The issue isn't that the costs were incurred, but that they were hidden. The bills were assigned to other departments, in order to keep the truth hidden. It's lying, and it's corruption.
It's always the cover-up that gets you. Ask Nixon, ask Clinton.
Rudy is a lot closer to Bill Clinton than he admits.
The analogy to Clinton is not apt.
Clinton used the police to procure women, and later used private detectives, managed by Hillary, to trash them.
Rudy used the police to protect his girlfriend, not to trash her.
Whatever you think of Rudy, it’s preposterous to say he’s as bad as Clinton. Nobody is as bad as “you might wanna put some ice on that” Clinton.
Good point. If Rooty tried to hide his actions, that's evidence of mens rea -- a guilty mind. He could justify his actions, and folks would be inclined to buy it. He's a likable dude, and NYC is a much nicer place to visit than it was before he took office. But if he's going to extremes to hide something, that raises the presumption that there is something to hide.
The expense was no big deal. If Giuliani took steps to hide the expense, then you just have to wonder why.