Superman can turn a relatively worthless chunk of coal into a diamond in only a few seconds effort. So the issue of paying for damages really shouldn't BE an issue, cause with an hour or two of his time converting coal to diamonds he could have probably paid for all of the 9/11 clean-up & repairs. The only issue of being submitted a bill should be the actual fairness of the bill, because EVERYONE knows people pad their bills, especially when it's greedy businessmen and politicians.
Diamonds are valuable because they're rare. If he makes them every time he causes damage, which would be a lot, their value would be that of most comic books these days. How do you submit a bill to someone who saves the world and your life?