Kerry County Council says its original cost estimate for the South Kerry Greenway didn't include land acquisition costs.
This was revealed in correspondence between the Department of Transport, Tourism and Sport and the local authority when funding was being sought for the proposed greenway in 2015.
The department also criticized the council's ability to construct the greenway “at any sort of a reasonable price.”
In documentation released to journalist Anne Lucey, in November 2013, Kerry County Council applied for funding for the proposed greenway under the National Cycle Network Funding Scheme 2014/16.
The local authority said the 32km greenway, from Glenbeigh to Renard, will comprise three phases and will be completed by November 2016 at a cost of €4.7m.
By June 2014, the council had been approved for €3.9m in funding, with the estimated cost still at €4.7m.
By June 2015, the cost had increased to €10m, by July it was €13.4m and by December of that year, it was €16.1m.
At last November's oral hearing, the cost of the proposed greenway was over €20m.
In the second quarter of 2015 - around the time of the increase to €10m - the council told the department its original cost estimates did not include the cost of land acquisition.
Last year, the oral hearing heard the council needs 115 acres to build the greenway.
The department also criticised the council internally; one official said in relation to costs “this is getting more ridiculous […] I'm rapidly losing faith in KCC's ability to construct this at any sort of a reasonable price.”