Sinn Féin says it can deliver 50,000 affordable homes within five years, if in government.
The party has published its Affordable Homes Plan, which it says will bring home ownership back into reach for working people.
The €13.2bn plan focuses on delivering affordable homes to people who earn too much to get social housing but are unable to afford current market prices.
Sinn Féin says affordable homes can be delivered at €250,000 to €300,000 depending on size and location – with the State paying for all land and related costs.
The party also aims to deliver homes to rent at or below €1,000 per month.
It says it will publish a detailed and fully costed five-year plan in early September.
Housing spokesman Eoin O'Broin explained that they could achieve the affordable purchase price by separating the cost of land and site servicing from the cost of building the home.
The party estimates that the State would be contributing 20-33% of all-in development costs, so that homes are more affordable through a Public Housing Fund.
Deputy Ó Broin said: "The State has to intervene decisively...to make affordable homes to buy but also to rent...and within the reach...of working people."
Under Sinn Féin's plan, affordable homes will be built on state land, the State would pay for the land and all related costs and retain ownership of the land.
While the purchaser pays the price of building the home and is the full owner of the property, if they want to sell it on, it must be within the affordable parameters.
They own the home and have the same rights as private purchasers to alter the property and pass it on to their children or grandchildren.
Government parties have long doubted the possibility of being able to deliver a home for €300,000, particularly in the capital.
But Sinn Féin leader Mary Lou McDonald defended the figure, saying: "It clearly is credible and deliverable. And we've run the numbers for you today. There was a debate around that figure, could it be achieved? And the answer is it can be.
"For a lot of people, they may have gotten into almost a space where they believe...my moment or my chance has passed.
"I'm never really going to own a house or have rent that I can cope with and that I can build a good life on, and I hope that this plan says very clearly to that set of people, and it is in the tens of thousands of people, that in fact there is an opportunity for you...to purchase an affordable home, to rent a home at an affordable rate."
Sinn Féin says the €13.2bn cost of the affordable housing programme would be split between €6.9bn in voted expenditure – i.e. exchequer funding, with the remainder coming from loans from the Housing Finance Agency, European Investment Bank or other low-cost loans.
The party’s plan says calculations are based on an average Public Housing Fund contribution of €103,000 per affordable purchase home and an average Public Housing Fund contribution of €155,000 per affordable cost rental home.
Sinn Féin has long grappled with the Government over its housing policy, which it says has failed.
The Housing Minister Darragh O’Brien has been quick to criticise the plan, saying the 14-page document lacked any new ideas and any detail on existing proposals.
Mr O’Brien said: "The failure to mention the Help-to-Buy, the First Home Scheme and the Vacant and Derelict Property Grant, which are key supports for First-Time Buyers and those seeking a fresh start, was further proof of the Party’s plan to take the legs out from under prospective buyers.
"These schemes combined are assisting more than 50,000 families and individuals in their home ownership journey."
Responding, Eoin Ó Broin said Minister O’Brien "should do his job he's had for years".
"He showed he can't, he's failed. And that's why we're setting out a very clear and radical alternative so people can make up their minds," Mr Ó Broin said.
"Do they want more of the same failed Fianna Fáil/Fine Gael housing policy that's locked an entire generation of young people not only out of homeownership, but they're losing hope they will ever be able to own their own home.
"That they have forced thousands and thousands of children into prolonged stays in emergency accommodation, or do they want a real detailed, comprehensive, costed alternative? Darragh should get on with his job, because the amount of time he has in that office is getting ever shorter."
Sinn Féin published the details of delivery costs for public housing last year, 2023, based on Parliamentary Questions provided by the Housing Minister.
It says that the level of Public Housing Fund contribution could be adjusted as the all-in cost of public homes becomes clear.
Part of the plan is to achieve economies of scale by ramping up public construction or direct delivery of homes.
