"We thought it might fetch $300 ... but [the auction] just went crazy," Mr Evans snr said.
"It started off, $300, $500, $700 ... and within about five minutes it was at $6000. And the auctioneer still pushing then, any advance on $6000. Everybody was sitting there aghast."
An Omaha resident eventually won the bid, but it wasn't clear why he was so keen on the teapot.
"He has three Ferraris - I don't think he's short of money. However, to spend $6000 on a crappy teapot."
The dinner at Omaha Golf Club raised about $25,000 to go towards a new hospice building.
Mr Evans said the media storm surrounding his Newmarket cafe following the politicians' conversation was "a bit of a fiasco", but ultimately good for business.
Television crews came to the cafe for a week after the meeting, and customers still asked about it. The cafe displayed one of the teapots in a case above the counter, and Mr Evans planned to put up a framed photo showing the politicians in front of a walled-out contingent of media.
Last night a spokeswoman for the Prime Minister said: "It is great that Urban Cafe's initiative has resulted in such a generous donation to this very worthy cause."
Mr Key and Mr Banks had believed their November 11 conversation, held at a staged media event, to be private, but it was recorded by freelance cameraman Bradley Ambrose.
The tape and its contents dominated coverage in the final weeks of the election campaign and helped New Zealand First leader Winston Peters to gain traction in the media. Mr Key laid a complaint with police over the tape.
The Attorney-General has filed a memorandum in the High Court at Auckland seeking $13,669.45 in costs from Mr Ambrose after the freelancer sought a declaration from the High Court on whether the "tea tape" conversation was private.