Forecast budget surpluses have been dramatically slashed to free up funds in order to soften the blow of Holden's closure, today's South Australian budget will reveal.

Treasurer Tom Koutsantonis said a $72 million surplus was now forecast next financial year, down from $382 million promised at last year's mid-year budget update.

Mr Koutsantonis said it was time for the Government to use its surpluses on new infrastructure, such as hospital upgrades, to create jobs.

"In 119 days Holden closes, in 119 days that transition is real for thousands of South Australians and now is time for the Government to step," he said.

"We've been building up to make sure those budget surpluses to spend when the headwinds are there."

The Government has outlined $315 million of spending at the Lyell McEwin, Queen Elizabeth and Modbury hospitals and the Flinders Medical Centre.

The site for the new women's hospital, which has been announced in this year's budget. ( ABC News: Tom Fedorowytsch )

A new $528 million Women's Hospital has also been announced, to be co-located at the new Royal Adelaide Hospital site.

South Australia already has the highest unemployment rate in the nation.

To address that, the budget also includes a boost to the job accelerator grant program, with small businesses who take on a trainee and keep them for two years to earn a rebate of up to $9,000 over two years.

Bigger businesses will receive up to $15,000.

SA budget about 'jobs of tomorrow'

Mr Koutsantonis described today's budget as a traditionally Labor one.

"That's what this budget is about, the jobs of tomorrow," he said.

"Over the last two years we have been creating jobs, but of course we are losing an anchor tenant.

"We projected to have $1.6 billion in surpluses at the mid-year budget review but we're spending, we're spending in the economy, we're building infrastructure and we're trying to create jobs."

Other budget announcements included an increase in first-home-buyer grants for off-the-plan apartments in the CBD to $40,500.

The Government also announced $22 million will be spent on extra passenger services on the Gawler, Seaford and Outer Harbor train lines.