Is that a firm price or a worst case estimate.
It's not uncommon that they go with the worst case estimate. If they tell you $7k and in the end it's $4k, you walk away happy that they got it done cheaper.
If they tell you $4k (their real best estimate) and once they open it up, it's worse, either they eat the cost difference or you get ticked off that it suddenly went up to $7k.
Getting a 2nd opinion is a good idea.
Without seeing the damage myself, hard to say if they are taking advantage of you or not.