Sandwell Council has been accused of wasting public money after admitting its benefit fraud investigation unit spent £517,000 last year but recovered just over half from illegal claims.
The running costs of the council's investigation team are almost double the £265,000 in illegally-claimed benefit payments the 15-strong unit managed to uncover.
It brought 80 prosecutions for unlawful claims.
The figures were uncovered through a Freedom of Information Act Request by the TaxPayers' Alliance.
Wage costs for the unit were £440,000, an average of £29,000 per employee and the cost of each prosecution worked out at £6,500.
The cost of running the operation was described as "astronomical" by TaxPayers' Alliance West Midlands spokeswoman Fiona McEvoy.
She said: "Obviously people who fraudulently claim benefit have to be prosecuted, but there is a value for money issue here. The salaries for members of the investigation team are well above the national average. Expenditure should be kept to an absolute minimum to avoid making taxpayers pay twice."