speaking of train wrecks, you can see the train that wrecked into the bus in the Fugitive (with Tommy Lee Jones). The train is still sitting next to the Tuckaseegee river near Dillsboro NC
That wasn’t a “single” joke. All in all, that set-up took double-digit minutes, what with the cannon, the rotations, the firing and what-all. Nailing the wreath to the door was just the capstone.
They mentioned this in the behind-the-scenes bit on the DVD–it’s a fake Shelby Cobra, but a fully functional one, so it’s still worth, like, $70,000. Just not a collector’s item, like Tony’s would have been. The guy who had to pull the trigger was distressed at having to trash such a nice car.
I nominate Buster Keaton’ famous falling-house scene from Steamboat Bill, Jr.. Not because of financial expense, but because of the potential expense of injury or death.
You’re right, of course. I should have “punchline,” not “joke.”
Keaton did lots of things that could have killed him. The famous sequence in The General where he’s picking up the ties that have been placed on the rail could have ended in disaster: he could have been caught under the engine, or if he hadn’t picked them up correctly the train could have derailed. It’s astounding the stunts he pulled off throughout his silent career.
Pontiac was made by GM. Did you mean Plymouth sister car?
For those not wanting to click blind links, this goes to a Super Bowl ad from the early 2000s where it just shows a monkey clapping for 30 seconds, followed by a graphic saying “We just wasted 2 million bucks”.
The piano probably cost more than the car. 
Maybe the KLF burning a million pounds?
Most expensive punchline
“I do”.
I believe he is confusing the Crossfire with the Pontiac Solstice/Saturn Sky. The closest to a sister car for the Crossfire was the first generation Mercedes SLK.
As I understand it, a lot of shiny new autos destroyed in movies and TV work are ones that the manufacturer doesn’t want sold, because they were built during production line startup, or otherwise don’t meet the company’s quality control.
Most such vehicles are crushed and shredded, but apparently there’s some channel to divert a portion of them to Hollywood.
To get back to the OP’s question …
One of the Roger Moore Bond movies (I’m at work, or I’d look it up) had Moore taxiing around an airfield trying to elude bad guys who were shooting at him. He drives into a hangar, and the bad guys at the other end of the building start closing the sliding double doors. Moore hits the partly open doors at high speed, and the wings are ripped off his plane, but the fuselage, with Moore inside, continues on to safety.
You can judge whether that’s a throwaway gag or not, but it certainly wasn’t the climax of the film.
Before the shot, the wings were sawn off the plane and stuck back on with chewing gum so they’d come off easily. That’s one plane that will never fly again But just in case they needed a retake, they sawed the wings off a second identical plane. They got the shot in one take, but two planes were destroyed.