Police Association president Chris Cahill said it was a bit of unknown if the money would be enough because there had not been a gun registry.
"We really have no idea how many of these firearms are out there in New Zealand," Cahill said.
"Which really points to how bad our firearms legislation has been, that we have let this get out of control."
The Government had signalled more money could be found for the buy-back scheme, if needed, he said.
"It's shown they are willing to put a significant amount of money up and that will be an incentive for people to abide by the law and hand their guns in."
The semi-automatic weapon ban was established after 51 people were killed in mass shootings at two mosques in Christchurch.
The weapons, including semi-automatic shotguns, were prohibited within a week of the terror attack, with legislation rushed through Parliament and passed within a month.
However, the ban excluded rimfire rifles .22 calibre or less, as long as they had a magazine that holds 10 rounds or less, and excluded semi-automatic shotguns that had a non-detachable, tubular magazine that holds 5 rounds or less.
Pump action shotguns capable of being used with a detachable magazine or possessing a non-detachable tubular magazine, capable of holding more than 5 rounds, were also banned.
Police have already said it would prefer to collect the guns, rather than have people with firearms queuing up outside police stations.
Budget 2019 concentrated on child wellbeing and law and order announcements were not the focus.
But there was extra funding, including $25 million to beef up efforts to stop boat people getting to New Zealand shores, $50 million for spy agencies the NZSIS and GCSB, and $13.4 million for next year's cannabis referendum.
Australia has criticised New Zealand for being too reliant on Australia to stop boat people from trying to get to New Zealand, though the Government has repeatedly said that there are few, if any, concerted efforts from people-smugglers to undertake the perilous journey to New Zealand's shores.
Further funds for the justice sector include $212 million towards building 16 remand homes over four years to house 100 young people caught in the youth justice system, which from July 1 this year will include 17-year-olds for the first time.
That package is part of a larger child wellbeing package, which also includes $26.7 million over four years for Oranga Tamariki's NGO partners to improve intensive intervention services.
That is aimed to help keep at-risk children at home, rather than entering or re-entering state care. This hopes to cover 150 families and 400 children in its first year.
As at March 31 this year, 6400 children were in state care.
Half a billion dollars over four years has also been set aside for new Oranga Tamariki national care standards that come into force on July 1 this year.
Part of that will fund 350 more frontline staff and social workers and 60 extra support staff for caregivers, and $70 million will go towards a special individual bag of items for those in care that provides books, laptops, toys, health products and sports gear.
The Government has already announced $153.7 million to help young people transition from care or youth justice services back into the community, a service that currently does not exist.
The Defence Force will be boosted with funds designated to future air surveillance capability with four Boeing P-8A Poseidon Maritime Patrol Aircraft to be aquired.
Training systems for the aircraft will also be aqcuisitioned, as well as infrastructure, mission support and other services required to operate them.
"This investment contributes to maritime domain awareness and response, one of the particular capability requirements identified in the Strategic Defence Policy Statement 2018," the Budge stated.
"It will enable the New Zealand Defence Force to continue to deliver air surveillance, resource protection, and search and rescue, increasing the safety and security of New Zealand, our region and our international partners."
A further $12 million will be dedicated to delivering better responses to emergencies by establishing a new national emergency management agency.
The agency will replace the existing Ministry of Civil Defence and Emergency Management.
Additional reporting Chelsea Boyle, Anna Leask
