The Government should have put more work into its initial costings for the proposed national cycleway, according to Labour leader Phil Goff.
Prime Minister John Key has indicated a 3000km national cycleway from Cape Reinga to Bluff would cost $50 million and employ 4,000 people.
The idea came out of the job summit in February.
But engineering consultants estimate the cost of the cycleway will be about six times that amount.
Trevor Butler, of outdoor recreation engineers Frame Group Ltd, says a concrete cycleway costs about $100 a metre, which would mean the proposed national trail would cost about $300 million.
That does not include costs for bridges, crossing points, signage or land purchase. Mr Butler also says that the number of jobs is unrealistic.
Mr Goff is questioning how the Government got the cost of the cycleway so wrong, saying more thought should have been put into the idea.
Mr Key says officials are working on options for the project.