If you have the DLC for Wrecking Crew use the following.
Mode: total chaos
weapon: Thermobaric Rocket
If your player starts on the ground you can easily get 280-325000
if he starts on the bridge you can get 250000 easily
just start by shooting all the braces at the ground where they meet. I started on the far ends then shot the ones in the middle and the bridge pretty much collapses on its own. You may need to shoot the bridge where it meets the cliff to help the ends fall.