2004 Mercury Monterey seats problems

While driving I noticed my third row seat was bouncing some, when I stopped I found that the latch holding the seat down was unattached. When I took it into the dealer he said that it is rusted through. I had my special needs son in that seat, hit his head but nothing major. Unfortunately I now am unable to transport my special needs son because he has to be in the third row seat. My drivers side wheel well is also totally rusted through and water is getting into the car.

Large section of driver side rear wheel well/underbody, broke off from vehicle including an anchor for the third row seat. This left the third row seat unsafe to use and the interior of the vehicle exposed to the elements. Piece was clearly rotted through. We are told it will cost $1200 to repair, parts are scarce and difficult to obtain. Unable to safely utilize third row seat until repaired. Water is trapped in the underbody and could be damaging to the electrical system. Pictures available upon request.