2006 Other Mazda Models Flood Damage

I recently got into an accident. I swerved to avoid an animal that was on the road and hit loose gravel and lost control of my car. It then flipped upside-down into an embankment that was flooded with water. The water drowned the engine completely up to the dash. It was towed. The car is structurally sound and there is very very little exterior damage. My left front corner panel where the door meets the sheet metal was dented in due to the tow company pulling the car out. I have not tried to start the car because I have heard that could cause more problems. When the battery is connected the lights and horn and windshield wipers start up. Is the engine lost? Will I need to get a new engine? What would be the most cost effective way to repair? Any advice would be greatly appreciated.