The bill for agency staff at Walsall Manor Hospital rose by more than £250,000 in a month, figures have revealed.
It increased to £721,000 as the overall cost of temporary workers increased to £1.6 million throughout June.
The combined level of expenditure on agency, bank and locum staff has continually risen since the start of the financial year.
It comes as it emerged nationally that NHS hospitals are so short staffed on public holidays they are paying almost £150 an hour for nurses to work. On May Day Bank Holiday this year a locum agency was paid more than £1,800 to supply a nurse for a 12-hour shift in Bristol.
Walsall Healthcare NHS Trust is recruiting 70 nurses to cope with demand on services with rising number of patients coming from Staffordshire.
The cost of temporary workers rose from £1.525m in May to £1.656m in June. Of this, expenditure on agency staff went from £454,000 to £721,000.
However, the amount used on bank staff dropped by £113,000 to £476,000 and locums reduced by £23,000 to £459,000 in the same period.
Part of the rise has been attributed to invoices for shifts worked in addition to those recorded within the bank system.
In a report to the trust board, head of finance Ian Baines, said: "The costs associated with nursing reflect the high levels of agency usage to service additional capacity, wards 12 and 14 and falls prevention.
"Plans have been developed to reduce expenditure and recruit permanently to the nursing establishment."
It emerged earlier this year that more than £1,400 was paid for one agency nurse to work a single shift.
The 12-and-a-quarter-hour Bank Holiday shift at the Manor cost the equivalent of almost £120 per hour.
Bills climbed as high as £2m last year and after a reduction the costs have started to increase again, going up each month since April.
Bosses have taken steps to try to tackle the use of temporary workers at the hospital.
They are recruiting for up to 70 nurses despite battling to make £10.7m of savings during this year, while expansion plans are pushing ahead.
Work on a new critical care unit will start this autumn after the £8.3m facility has received the go-ahead from the Trust Development Authority. Health chiefs are hoping it will be completed by early 2016.
The planned West Wing unit will combine the high dependency and intensive therapy departments and have 18 beds.