How much are your private conversations worth to the government? Turns out, it can be a lot, depending on the technology.

In the era of intense government surveillance and secret court orders, a murky multimillion-dollar market has emerged. Paid for by U.S. tax dollars but with little public scrutiny, surveillance fees charged in secret by technology and phone companies can vary wildly.

AT&T, for example, imposes a $325 “activation fee” for each wiretap and $10 a day to maintain it. Smaller carriers Cricket and U.S. Cellular charge only about $250 per wiretap. But snoop on a Verizon customer? That costs the government $775 for the first month and $500 each month after that, according to industry disclosures made last year to Rep. Edward Markey, D-Mass.

Meanwhile, e-mail records such as those amassed by the National Security Agency through a program revealed by former NSA systems analyst Edward Snowden probably were collected for free or very cheaply. Facebook says it doesn’t charge the government for access. And while Microsoft, Yahoo and Google won’t say how much they charge, the American Civil Liberties Union found that e-mail records can be turned over for as little as $25.

The industry says it doesn’t profit from the hundreds of thousands of government eavesdropping requests it receives each year, and civil liberties groups want businesses to charge. They worry that government surveillance will become too cheap as companies automate their responses. And if companies gave away customer records for free, wouldn’t that encourage gratuitous surveillance?

But privacy advocates also want companies to be upfront about what they charge and alert customers after an investigation has concluded that their communications were monitored.

“What we don’t want is surveillance to become a profit center,” ACLU principal technologist Christopher Soghoian said.

Regardless of price, the surveillance business is growing. The U.S. government long has enjoyed access to phone networks and high-speed Internet traffic under the U.S. Communications Assistance for Law Enforcement Act to catch suspected criminals and terrorists. The FBI has pushed technology companies like Google and Skype to guarantee access to real-time communications on their services.