The NRL's Dally M leader made the stunning pledge after leading Cronulla to their fifth straight win on Sunday, a 22-16 home triumph over Canterbury that vaulted the Sharks into fifth spot.
"If they can make it happen, I'm not just going to go out there - I'd play for free. I'll donate my money to charity. I don't really mind," Fifita told Triple M radio.
Fittler earlier said he wouldn't rule out selecting Fifita for game one of the series in Melbourne on June 6 despite the tearaway front-rower being unavailable for Origin II on June 24.
Fifita can't play because of his allegiance to Tonga, who play Samoa in a Pacific Test in Campbelltown, the night before the second Origin game.
"There's nothing more in the world I want (than) to win a State of Origin series," said Cronulla's 2016 grand final hero and 2013 World Cup winner with Australia.
"I've never won one before and, look, I'd love to win one.
"I wouldn't let the team down. My heart is through and through a blue.
"If we get that series win and I get that under my belt and I have that series win to my name, I've done pretty much everything in the game."
Whether others in the NSW camp see it the same way remains to be seen, despite a softening in stance from Fittler.
NSWRL officials last week told AAP that Fifita would not come under consideration because he had elected to play in the Test.