I just read in the news that Hollywood Reporter asked a damage assessment company to check how big the cost would be to rebuild the city after the Avengers saved it.
The company used computer models for analysis, and in their final paper the number goes to 160 milliard $. They also talk about who should pay for this. SHIELD is a secret organization, so they are out. Probably a part would fall for the heroes mostly Hulk, at last what can be demonstrated was done by him with evidence. Things get complicated as most insurance companies have a clause about war, or terror act happenings. Also since in some cultures Loki and Thor count as Gods, their destruction counts as "act of God"... LOL XD
The article in Hungarian can be read
here.