A locum doctor at Stafford Hospital was paid £5,667 for a single 24-hour shift, it has emerged.
Mid Staffordshire NHS Trust said it was unexpectedly faced with the prospect of having no A&E consultant on 20 March and hired agency cover at short notice.
It said it was "disappointing" to pay high agency fees, but it always put the safety of patients first.
Cure the NHS patient group said it was an unacceptable amount to spend on any staff and rotas needed to be improved.
Hospital director Julie Hendry said new on-call rotas were being devised to help avoid a repeat situation.
The director of quality and patient experience at the hospital added: "If at very short notice somebody goes off sick or a member of staff is unavailable, clearly we cannot leave patients at risk.
"However we will be planning to ensure that does not happen again."
Manjit Obhrai, medical director of the trust, said the need to hire agency staff had been increased by the introduction in 2004 of The European Working Time Directive for trainee doctors, which limited the number of hours they could work.
He said: "In these circumstances we always put patient safety above cost.
"This means that we have to pay the going rate for those staff who are available to cover, sometimes at short notice. These costs are often extremely high, due to the agencies' fees."
Julie Bailey, of Cure the NHS, said: "It's not good enough that anyone should be paid that sort of money. Something has gone wrong here with the rotas and it needs to be fixed."
A new hospital management team was brought in when it was revealed in 2009 that up to 400 more deaths had occurred at the hospital between 2005 and 2008 than would normally be expected.
Ms Bailey said: "They are supposed to be the top management team in the country but they are making mistakes like this, it is not good enough."