Long-running optimisation studies have reduced the capex from US$832 million to $505 million, including a 15% contingency.
Greenland said the project now had the lowest capital intensity of all ASX-listed rare earth projects.
The figure includes a refinery circuit, though improvements to the flowsheet have reduced the scale of the circuit.
A previous study in 2016 had Kvanefjeld producing a 14% rare earth oxide, but work completed since then has increased that to 22%.
Civil construction and port cost estimates were also updated and lowered.
At the same time, annual production has increased to about 32,000t of REO, including 6000tpa of magnet metals neodymium, praseodymium, terbium and dysprosium.
"With the completion of an outstanding optimisation program, we have a project with a smaller footprint producing more rare earths at lower operating costs, which requires significantly less capital for development," Greenland managing director Dr John Mair said.
"The 40% reduction in the capital cost estimate together with the increased projected output over an initial 37‐year mine life results in the lowest capital intensity amongst our peers.
"The optimised capital costs, when considered with operating costs after credits of below $4/kg of rare earth oxide, creates a highly robust project and compelling development opportunity; a strong result for both company shareholders and project stakeholders."
Using spot prices as of July 4, the basket price for product is $15.32/kg REO, up 16% since May.
Greenland's forecast prices, based on Adamas Intelligence forecasts, has the basket price at $19.55/kg REO.
Greenland has a memorandum of understanding with major shareholder, China's Shenghe Resources Holding Co, for commercialisation of the project.
Shenghe collaborated on optimisation studies.
The non-binding MoU covers rare earth separation, offtake and marketing, and project finance.
Shares in Greenland were up 7.1% to A15c, after hitting a two-year high of 16c earlier in the session.