Nursing staff from a private employment agency are costing health trusts in Northern Ireland up to £736 per shift.
A trade union said the "excessive" spending on stand-in nurses was a "consequence of failures in workforce planning".
The DUP, which obtained the figures through Assembly questions, urged the Health Minister to tackle the "hugely inefficient" use of agency cover.
Robin Swann said trusts employ locum staff for a variety of reasons and the spending can "ensure that safe and effective services are sustained".
The figures looked at health trust spending on staff from the Scottish Nursing Guild on three dates in October.
More than £115,800 was spent on nurses covering 188 shifts from Saturday October 9 to Monday October 11 - an average of more than £615 per shift.
The Western health trust had the highest spending per shift at just over £736, followed by the Northern trust at £652.
The South Eastern trust spent £601 per shift on average, the Southern trust figure was almost £575 and the Belfast trust spent £515.
According to its website, staff employed in Northern Ireland via the Scottish Nursing Guild can earn between £16.50 and £93 per hour depending on shift times, dates and specialisms involved.
DUP MLA Deborah Erskine, who sits on Stormont's health committee, praised the work of nurses but said the figures showed health trusts are "failing to manage their workforce".
She added: "Setting aside the hugely inflated costs for shift cover, how does a shift in one trust cost £200 more than in another?
"I have spoken to scores of nurses who are hugely experienced, but they work for agencies rather than full-time in the trust as it suits their work life balance."
Mrs Erskine said while agency work is better paid, not all of the trust spending would go towards staff wages.
She said: "I have asked the minister to bring forward proposals which would end the hugely inefficient use of agencies and make the job better suited to the needs of the workforce.
"This is not the fault of our hardworking nurses - this is the fault of management."
The Royal College of Nursing said expenditure on agency nursing and midwifery staff in Northern Ireland has almost doubled in the last two years from around £52million in 2018-19 to more than £110million in 2020-21.
Northern Ireland director Rita Devlin said: "The RCN has highlighted for many years how excessive levels of expenditure on agency nursing are a consequence of failures in workforce planning and an inability to recruit and retain the numbers of nursing staff that we need to provide safe and effective care.
"Nurses did not create this over-reliance on agency staffing and the RCN recognises that many nurses legitimately choose to work on an agency basis for a variety of reasons."
However, she said the level of spending was "simply not sustainable".
In response to Assembly questions, Mr Swann said: "Trust expenditure on agency staff has been incurred to ensure that safe and effective services are sustained and contributes importantly to maintaining service provision to patients and clients."
The minister said trusts employ locum staff for reasons including cover for sickness; maternity or paternity leave; existing vacancies; and increased demand over the winter months.
He added: "The primary aim of this is to ensure that safe and effective services are sustained at all times for patients and clients."
The Scottish Nursing Guild was approached for comment.
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