Transport chiefs have insisted the revised MetroLink project represents value for money, despite not concluding a cost assessment of the plans.
The scheme linking north county Dublin with Sandyford in the south via a light railway was originally estimated to cost €3bn.
It was revised because of concerns among residents in south Dublin about disruption to Luas services during construction.
The new 19km route, with one tunnel instead of 26km with two tunnels, has not yet been fully costed, despite being shown to the public this week.
National Transport Authority deputy chief executive Hugh Creegan told the Oireachtas Transport Committee yesterday he is confident the revised MetroLink project will represent value for money.
He said a "robust" estimate was being prioritised and a business case will be available later this year.
Once this was ready it would be shared with the public.
Changes to the original metro design mean it will now terminate at Charlemont, south of Ranelagh, and link with the Luas green line, after residents protested over disruption they would encounter during construction.
It had been due to run farther south, to Sandyford, from Swords in north Dublin.
Stations at O'Connell Street and St Stephen's Green have also been moved slightly to minimise disruption.
All the changes will have an impact on cost, but Mr Creegan said a cost-benefit analysis had not been carried out yet.
"We have done enough work to satisfy ourselves that there is a very high level of passenger flow with people interchanging at Charlemont," Mr Creegan said.
"To get an accurate and fully developed cost estimate you need to have settled on the design and you need to have the design further developed.
"We are still in a consultation. You can see the changes from the first phase to now.
"It is our intention that when we get the design moved on further we will go about preparing a business case and later this year we will develop a very robust and solid cost estimate."