"But well beyond that would not surprise me."
He said the most a Goldie had sold for was at auction in London, where the top bid reached about $960,000.
In November 2013, the International Art Centre sold Goldie's first painting for $732,000.
Mr Thomson said the artist's last piece was in some ways more significant than the first.
"After fifty-odd years of painting, he's perfected his technique," he said. "This is Goldie at his very best, it's absolutely priceless."
Mr Thomson said Goldie's lifetime of artistic prowess was "very much at the heart of our national artistic history and identity".
"He's so iconic, everyone remembers him, it's a magic name in the art world."
Goldie stopped painting in 1941. He died six years later in 1947.
Other works of significance at this evening's auction included pieces by Peter McIntyre, Colin McCahon, Evelyn Page and Frances Hodgkins.