How much does the government pay for secret surveillance?

How much is your data worth to the government? Turns out, it can be a lot.

Government surveillance has developed into a murky, multimillion-dollar market with little public scrutiny. Fees charged by telecommunications and tech companies for the FBI or National Security Agency to access data are levied in secret and can vary wildly.

According to documents reviewed by The Associated Press, the average telephone wiretap costs the government more than $50,000, with big federal cases running as much as $2.9 million.

Facebook, meanwhile, says it provides access for free, while Yahoo and Google are estimated to provide email records for as little as $25.

Civil liberties advocates say they want companies to be upfront about what they charge and eventually alert consumers that their communications were monitored.