Thor is there because he wants to help. He isn't getting paid. He's not actually an Ultimate. Stark is using all his money and power to help people. The Iron Man suit costs him a lot to use.

The Authority still risked their lives to save the world, damn it.

Thing is- I can’t spell or type. I spell so badly my spell check doesn’t even know what I was trying to spell. And I have five Eisners HAHAHAHHA!! -Brian Michael Bendis