Then you have left yourself no recourse but to accept whatever arrangement this shop and the insurance company come to.

 

Sorry to say but you should have had it towed to the Porsche dealer and had them do all the analysis. Then the insurance would have to work with them. The insurance may not be willing to pay what the dealer charges but at least the car would be fixed properly. You would then need to cover the rest. I would after this probably switch insurance companies if you are paying for full coverage. But it is surprising the insurance is entertaining this at all considering you told them that you willingly drove through when the water was as deep as the headlights. I would have reversed if I could as soon as realizing the water was getting deeper, I am sure you were not doing 60mph through this water so it would be easy to tell whether it is getting deeper or not.