Superbowl performers don't get paid anymore... Well, they get paid a couple grand but that is only due to union requirements. But, that's it.
NFL pays for stage, lighting, logisitics.
If a performer wants to make the show "special", they have to pay out of their own pocket. In 2021 "The Weekend" spent $7M of his own money to enahance the show.
Swift has > $1B and could afford to spice the show up.