The search for Ben Needham cost £513,221 last year, new police figures reveal.
The cost was disclosed by South Yorkshire Police following a request under the Freedom of Information Act.
The year before the force spent £38,031.
A South Yorkshire Police spokeswoman said: "The spend includes travel, equipment, professional fees and officers' time whilst working on the investigation."
The amount spent so far this year, including excavation work carried out on the Greek island of Kos over the last three weeks, has not yet been revealed.
Ben disappeared from outside a farmhouse his grandfather was renovating on July 24, 1991.
His family always believed he had been abducted but this week detectives said they believe he died as a result of an accident.
It is suspected that Ben, who was 21 months old when he vanished, was crushed and buried by a digger which was clearing a building plot close to where Ben was playing.