Some - particularly Indigenous and Torres Strait elders - were ignored, Australian Council of Social Service (ACOSS) chief executive Cassandra Goldie told reporters at Parliament House on Wednesday.

Excluded from the budget lock-up on Tuesday, they are querying the missing budget dollars that could close the gap on family violence, health, housing, jobs, income support, and deaths in custody.

"The First Nations leaders, they want to be heard," Dr Goldie said.

The groups want community-controlled dedicated funding for services, including early-childhood education and care, uncoupled from activity tests, because it is meant to be about the children not just a work measure.

Dr Goldie warned of a "two-world Australia" where $7 billion more had been committed for tax cuts while others were completely unable to afford any kind of safe, secure place to live.

President of People with Disability Australia Sam Connor, who is autistic, has ADHD and muscular dystrophy and uses a wheelchair for mobility, slammed the "scare campaign" about the cost of the National Disability Insurance Scheme.

"First it was about prostitutes and yachts, and things that didn't happen, and now it's about cost blowouts," she said.

A $4.2 billion underspend on the NDIS helped the government's coffers in 2018/19, shrinking the deficit.

"It's shameful that most of the people we speak to on a daily basis say they can't access the NDIS and they are grossly underfunded on their plans," Ms Connor said.

Extra funding will see the scheme hit $31.9 billion by 2024/25 and Mr Frydenberg pledged in his budget speech that the NDIS would always be fully funded under a coalition government.

The federal budget assigned $2.3 billion to mental health over the next four years, including $298 million for suicide prevention and support.

But Mental Health Community Coalition ACT chief executive Bec Cody said the treasurer "completely missed the mark on community mental health".

There are 450,000 people living with psychosocial disorders that are not receiving support under the NDIS.

Ms Cody said it was excellent that acute mental health units would be built but questioned what help there would be for people in regional, rural and remote areas of Australia.

There is also concern about the budget saving of $671 million over five years by forcing new migrants to wait four years for any welfare payments.

"We're hearing pain across the community," head of the Equality Rights Alliance Helen Dalley-Fisher said.

Australian Associated Press