[Phantasm]

Well, Tony only really ever pays for superhero battles the Avengers as a whole are involved in, and usually he pays Damage Control to handle it (pretty sure he owns stock in the company...)

Other superhuman battles, such as X-Men vs Juggernaut? He doesn't often get the bill or promise to pay for those, though I don't doubt he helps with the cleanup.

One interesting factoid I came across in the 1989 Official Handbook entry for Damage Control was that New York City has been declared a permanent FEMA Disaster Area due to the high number of superhuman battles there, meaning the federal government helps pay for damages from superhuman battles. Yes, your taxes go to pay for cleaning up after the superheroes and supervillains.....