Jonathan Ross is one of the corporation's top earners
BBC radio shows cost "significantly" more than those made by commercial stations because of the large salaries of presenters, a watchdog has said.
The National Audit Office, in a report commissioned by the BBC Trust, said 79% of drive-time show and 77% of breakfast show costs related to presenters.
It also found cost variations across BBC stations - Radio 2 music programmes cost 54% more than those on Radio 1.
The watchdog's report looks at the efficiency of the BBC's radio output.
The report also found that in-house radio dramas made in London and Manchester were at least 50% more expensive than those made in other regions.
The report said: "In addition, for most breakfast and evening drive-time programmes on network stations, the BBC's costs are significantly more expensive than commercial programmes in the same slots.
This was "largely because of the costs of presenters and other staff", it said.
Last week, the BBC confirmed the salaries of its stars would be reduced when their contracts next came up for renewal because of the economic downturn.
Last year, some salary details were leaked to the press, including a three-year deal for Jonathan Ross reportedly worth £18m.
Other figures suggested that Radio 2's Sir Terry Wogan got £800,000 a year, while Radio 1 breakfast host Chris Moyles took home £630,000.
For Thursday's report, the BBC refused to give the NAO access to specific presenters' salaries without an agreement not to disclose those figures publicly in the report.
NAO head Tim Burr refused to enter into such an agreement, saying it would place constraints on the watchdog's ability to report its findings.
The NAO said the BBC's radio services had found £11.7m efficiency savings, beating a target of £11.6m.
But it urged the BBC to compare its costs with commercial stations.
Tim Davie, director of BBC Audio & Music said: "I welcome this report and am pleased it recognises the £86m we are already committed to saving.
"However, there are clearly opportunities to do more and I am determined to increase efficiency while maintaining the unparalleled quality of our programmes."
Conservative MP Edward Leigh, who chairs the Public Accounts Committee, said it is "scandalous" that the BBC does not disclose presenters' salaries.
He added that the BBC's attempt to set conditions on supplying information to the NAO was "equivalent to imposing a gagging order".
"It goes to show the utter inadequacy of the current arrangements for parliamentary scrutiny of this publicy-funded organisation," said Mr Leigh.