A Freedom of Information request revealed the force picked up the tab for the six-figure sum in overtime payments, cars, and fees for a consultant .
The lengthy corruption inquiry by the police watchdog is believed to have cost between £5-7 million when taking into account officer and staff costs plus legal fees.
Staffordshire Police as the force under investigation had to pay the £308,917 costs racked up by the investigating team, known as Operation Kalmia, headed by Derbyshire Chief Constable Mick Creedon.
The Independent Police Complaints Commission (IPCC) probe saw 14 officers – including current Staffordshire Chief Constable Jane Sawyers – placed under investigation after five men jailed for murdering the amateur footballer had their convictions quashed in 2012 following serious police failings being revealed.
The IPCC's investigation was concluded two years ago. Only one junior officer has been reprimanded with the others facing no disciplinary hearings despite the IPCC recommending there should be further action taken against a string of top officers.
Staffordshire Police and Crime Commissioner Matthew Ellis today described the amount of money spent as 'obscene'.
He said: "It has been a poorly-run investigation which has cost millions of pounds of public money.
"The amount of cost that has fallen on Staffordshire Police is significant but not huge when you consider the overall cost of Operation Kalmia.
There needed to be an investigation but in hindsight the money could have been spent better. The total figure of between £5m and £7m is quite obscene when you consider there has been little public benefit.
"To put this into context on my second day in office back in 2012 I had an induction into Operation Kalmia and we are still dealing with it now. It has been a mess from start to finish."
Kevin Nunes, 20, from Whitmore Reans, was shot five times in a country lane in Pattingham in 2002.
Five men were jailed for life in 2008 but then had their convictions quashed after it emerged a key document that detailed serious failings in police investigation had not been disclosed at the original trial.
Last year the Express & Star won a major Freedom of Information battle with Staffordshire Police to have the secret report released.
Our own three-year investigation into the case revealed one of the detectives had an affair at the key witness's safe house and that crimes committed by the witness were covered up before the original murder trial.
A Staffordshire Police spokeswoman said the 'managed' IPCC investigation was launched following the Court of Appeal decision.
She said: "Whilst this investigation was independent, protocol outlines that the host force's costs are paid by the force being investigated (Staffordshire Police).
"Whilst there is scrutiny from financial audit, control of specific spend lies with the investigating force.
"The figures provided are accurate and include vehicle hire and fuel over a seven year period, as well as professional fees for two people, one of which was a consultant."