This is a problem that I would take to a shop that specializes in automotive electrics rather than to a dealer. I don't know what they mean by "main electrical system"
You may well have cooked a whole bunch of things. It would not surprise me at all if you end up spending $1500 euros or more. Just be glad your car is not the current generation of BMW with a half-dozen always-hot computers.
The fact that the car won't start worries me. Do the warning lights in the dash illuminate normally and does the engine crank when you turn the key?