The government is being urged to invest more than £28m in foster care in Northern Ireland.
Fostering Network said the study showed a shortfall
It follows a report which said this figure was needed to bring quality to the sector which has a shortfall of at least 350 carers in NI.
The Fostering Network and BAAF are to launch their Cost of Foster Care report at Stormont.
The network's Robert Tapsfield said: "We have robust calculation of what providing foster care costs."
He added: "It demonstrates that there is a massive shortfall."
The report assesses the spending required to give children in public care the same opportunities "to have a successful future as other children".
It draws on the experiences of an expert working group from health boards, trusts, independent fostering agencies and local authorities.
The Fostering Network said the study showed a shortfall of at least 350 foster carers across Northern Ireland.
This contributed "to the lack of choice for children, placement disruption and further instability", it said.
"This is a call to the Northern Ireland government to invest a further £28.5m in foster care services each year," said Mr Tapsfield.
"We should ensure that the outcomes for children in foster care are the same as those we want for our own children."
Felicity Collier, chief executive of BAAF, said there was "an overwhelming need to do better for children in public care".
"It is simply not good enough that there is no choice of foster carer for so many children, and that foster carers are not paid a living wage throughout the year so that they can be available when needed.
"The report makes the case for planned long-term investment in the children who are at risk of becoming the parents of tomorrow's poorest children instead of happy, economically active citizens."