I do not know about the costs involved with this happening, but a friend of mines father runs a repair shop and does up to meduim duty recovery. They were called to a truck that had sunk in a pond about 300yards from the road. The truck (brand new, less than a month) was started in the morning by the owner and the parking pin failed, the truck rolled out of the driveway, across the street, down an enbankment and into the pond behind his neighbors house. It took two wreckers and about 5 hours, total bill was just under $5,000. Pictures here
http://www.loudongarage.com/gallery/recoveries.shtml It is the December 29, 2004 slide show.
I would have to think with fines and diving costs that that amount would at least double.