The Japanese, whose comeback was announced by the tail-end team on Tuesday, said he met owner Tony Fernandes at a Queens Park Rangers soccer match in London in December and said he just wanted to drive.
"I am free. You get more money than me," he told Reuters with a grin after his presentation to staff at the Caterham factory in central England.
"We paid with my fans' donations and I have to really thank my Japanese fans. I think I could not get this seat without my fans.
"I don't need money. I just want to drive. I don't care about money. I want to be a success in my life and bring the team that success. This is my goal."
Kobayashi, the only current Japanese F1 driver, set up a website in 2012 to get him back on the grid at at a time when more and more teams were looking for drivers with financial backing.
It was too late for 2013 but he kept on plugging away while racing in sportscars with a Ferrari team.
Fernandes, he said unsurprisingly, was quite happy with the zero salary arrangement.
The Malaysian airline entrepreneur, who also runs QPR in the second tier of English soccer and had been interested in signing Kobayashi before he went to Sauber in 2010, said the money had not been a consideration.
Fernandes felt sure Kobayashi, a fan-pleasing driver who last raced in Formula One in 2012 when he finished third in his home Japanese Grand Prix with Sauber, was just the man to shake up the team.
"Whether I get a million, half a million or save two million, in the scheme of things makes no difference when you are talking about 80 million pound ($131.36 million) budgets," the owner told reporters.
"What we thought Kamui brought is maybe that little bit of spark. Something you can't really quantify, that maybe just motivates the rest of the 250 people to say 'we've got a chance now, we've got a warrior who is going to go in there and do whatever to move this team on'.
"That's the main reason we've taken him. We've seen on the track, it's well-documented that he goes for it. My message in signing him is to tell the people...that we've got to go for it. This is it."
Fernandes said there were also business advantages in signing Kobayashi, with an Asian-owned team having an Asian driver and possibly bringing in some new backers.
Even then, it was the driver's fighting spirit that stood out and changed his mind after he had previously been on the verge of bringing back Finland's Heikki Kovalainen.
"There's something in his eyes. He was hungry," he said of the Japanese who had a few rough edges in his time at Sauber but thrilled fans with his daring and eagerness to at least try and overtake. "And I want everyone in this team to be hungry.
"It might be a disaster in some races but I'd rather die trying than not try."
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