New South Wales's peak farming body says the damage bill for wheat losses alone in the state's flood-hit north-west will surpass $150 million.
Parts of Moree, Gunnedah, Dubbo and Moama have been evacuated as more than 140 flood warnings remain across the state.
Agronomists say the grain-growing hub of the north-west is expected to have "conservatively" lost more than 120,000 hectares of wheat that was nearly ready to harvest.
The region also boasts large barley and canola outputs and is in the summer planting window for crops such as cotton and sorghum.
The NSW Farmers Association is calling on the federal government to bolster flood support payments in Labor's first budget in this term of government.
The lobby group's Grains Committee chair, Justin Everitt said the dollar value of the wheat damage is on top of approximately $42 million farmers spent to grow the crop, in a year where input costs have been extraordinarily high.
He said crops are "now drowning beneath floodwater" and may be a "complete write-off" if paddocks don't dry out soon.
"You spend all this money preparing your paddocks, sowing your crops, fertilising and spraying them, only to see them wiped out a couple weeks before harvest. It's heartbreaking," Mr Everitt said.
"Farmers know they're taking a bit of a gamble when they're planting a crop, but this ongoing wet weather with flood after flood after flood is just unbelievable."
Moree Plains deputy mayor Susannah Pearse said the bumper crops have been devastated.
"It's the fourth biggest flood in our history," she said.
"It's not what we needed as we head into our winter crop harvest.
"Ordinarily we're the most productive agricultural shire in Australia. Typically, we get about $1 billion of produce from the Moree Plains each year.
"It's going to have a huge impact on our community, we're really heavily dependant on agriculture.
"When agriculture does well, the Moree township does well."
Budget make or break
John Lowe, who leads the NSW Farmers' Business, Economics and Trade Committee, has called on the federal government to increasing flood relief payments in Tuesday's budget.
"There are many impacted farmers who will be cash poor and without an income as a result of this flooding, and that has caused widespread economic pain across rural areas," Mr Lowe said.
"So many of our towns and businesses depend on agriculture, so it is critical farmers have the certainty to try again next season.
"Swift financial assistance – or the lack thereof – could make or break many farming communities."
Future could be 'financially disastrous'
Mr Everitt said the flooding was unlikely to directly impact food prices in the short-term, but it could lead to 'cash droughts' for farmers in the region moving forward.
"As they try to find the money to clean up and go again – the soil will be ready, but they may not be able to afford to plant in it," he said.
In some parts of the north-west such as Wee Waa, crops have been submerged for weeks. For those properties not underwater, many farmers have struggled to work machinery in sodden paddocks and to move around under impacted roads.
"We've had a huge crop across the state in those places where people could get on paddocks to sow, but now that's all under threat too," Mr Everitt said.
"It's a big turnaround in fortune from the big bumper harvest ABARES was predicting a couple of months ago.
"If we don't dry out soon, it will be financially disastrous for a lot of growers."