I would do this swifty and matter-of-factly. The longer you wait, the more resistance you're gonna get because they'll come up with all kinds of self-righteous justifications to get out of it. I'd have the car towed to a good Z shop or dealer, get a written quote and stick it right in the faces of those pricks that drove your car. If they balk, ask them if they'd like to go to court over it as you'd be willing to run down to the courthouse and file against them right NOW.