2008 Audi TT Question 6 cyl Automatic

I'm a driver from Hanoi, Vietnam. I've got an Audi TT Estronic 3.2L, engine V6. Recently, there was an heavy rain in Hanoi made all streets flooded in deep water. I drove my car at night, when it was still raining and the street lights were off, ran through water but couldn't make it so the engine stopped, i tried to re start the engine once but couldn't so i stopped ( coz i heard about the problem of if you're keep trying to start the engine, the piston set might be bent). Right afterward, i asked some guys to push my car to the peak so avoid the flood, but still the water already get into my cabin and the car wont start. Yesterday, i took my car to the garage but they said i'm in big trouble now bcoz the water flooded in the engine and electrical box (no idea what it's, the only thing i know that electrical box thing is under the driver's seat). So I'm writing to ask what exactly happened to my car and the guy in the garage said i have to do some replacement for the engine, is that true ??? if it's , then how much would i have to pay in total, approximately ???