It's goshdarn expensive, as reported by Associated Press via Star-Tribune:

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.

Email, unsurprisingly, is cheaper:

Meanwhile, email records like 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 email records can be turned over for as little as $25.

How much in total is this costing us taxpayers? Ah, no one knows:

The FBI said it could not say how much it spends on industry reimbursements because payments are made through a variety of programs, field offices and case funds...

At least it's creating jobs!

 AT&T, for example, said it devotes roughly 100 employees to review each request and hand over data. Likewise, Verizon said its team of 70 employees works around the clock, seven days a week to handle the quarter-million requests it gets each year.

And some stuff comes for free:

Most companies agree not to charge in emergency cases like tracking an abducted child. They aren't allowed to charge for phone logs that reveal who called a line and how long they talked — such as the documents the Justice Department obtained about phones at The Associated Press during a leaks investigation — because that information is easily generated from automated billing systems.

An average wiretap costs $50K, and one narcotics case in NYC cost $2.9 million--money well spent, I'm sure.