There will be speeches and cake, but it won’t be a celebration when Newstart recipients gather outside Josh Frydenberg’s office on Thursday.

The cake is to mark a milestone: the 25th year that a government has failed to lift the dole in real terms. It currently stands at $277.85 a week for single people – about $40 a day.

The speeches will touch on the experiences of more than 250 Newstart recipients who are members of the Australian Unemployed Workers’ Union.

Some tell of sleeping in their cars, eating “substandard” food or skipping meals altogether, and living in constant fear of becoming homeless. A number make desperate allusions to the state of their mental health.

“Camping with a chronic illness in winter is incredibly tough, and the cost of a campsite is more than what rent assistance can cover, which is ridiculous,” says one.

Another says simply: “I have been in a sexual relationship just to have a roof over my head.”

The responses will be stuck to the front window of the treasurer’s office by protesters on Thursday morning. Frydenberg will be in Canberra for the final day of parliament before the election, two days after he announced a projected budget surplus of $7.1bn.

Frydenberg also revealed on Wednesday the government would extend a planned $75 energy supplement payment to people on Newstart. They were left out of the budget.

Asked why the Coalition had again declined to lift the unemployment benefit, the prime minister, Scott Morrison, said the government was “getting them into work” instead.

“The difference about Newstart Allowance is that people on Newstart aren’t intended to be there for a long period of time and they also have access to a range of other income support payments,” he told ABC News Breakfast on Wednesday.

An Acoss report last year found 44% of people on Newstart were on it for more than two years and 15% for more than five years. The welfare peak body’s proposal to lift the payment by $75 a week would cost the federal budget $3.3bn a year, while boosting consumer spending, Deloitte said last year.

“We’re bringing with us hundreds of letters and notes from our members – Newstart recipients – who wanted treasurer Frydenberg and his government to know what it’s like to survive on an entitlement of $243 a week below the poverty line,” said Jeremy Poxon of the Australian Unemployed Workers’ Union.

“Even we were blown away by how much they are suffering.”