Special counsel Robert Mueller secured a win last Friday, with President Donald Trump's former campaign manager, Paul Manafort, pleading guilty to conspiracy charges and agreeing to cooperate with the ongoing investigation.

Mueller may have also paid for his own investigation.

That's because, as part of his plea deal with the special counsel, Manafort agreed to forfeit real estate and cash estimated to be worth between $42 million and $46 million. The special counsel's office declined to provide an estimate for the value of the assets.

Those properties include Manafort's Trump Tower apartment, two apartments in lower Manhattan worth about $3 million and $4 million, a brownstone in Carroll Gardens, Brooklyn, and his sprawling 10-bedroom mansion in the Hamptons section of Long Island.

Manafort will also give up money in three bank accounts and in his life insurance policy.

In all, the value of the real estate alone that Manafort is surrendering amounts to an estimated $22 million. The exact value of the assets will not be known until it is all sold. The federal government routinely auctions off forfeited goods and contracts with real estate brokers to sell seized properties.

A Justice Department official told NBC News that the money will not go directly to funding Mueller's probe. But supporters of the investigation were quick to note that the seized assets address a central criticism that Trump and his allies have levied against the inquiry.

In May, shortly after joining Trump's legal team, former New York Mayor Rudy Giuliani blasted the cost of the probe, saying that Mueller "wasted $20 million on an investigation that begins without any evidence and ends without any evidence."

In June, Trump wrote in a post on Twitter that "the Russian Hoax Investigation has now cost our government over $17 million, and going up fast."

Even members of Congress were pushing the talking point.

"The least we can do is start looking at all the ways he's absolutely blown taxpayer dollars," Republican Rep. Louie Gohmert said on Fox News in June. "He's wasted money right and left."

It was a line of argument heard across conservative channels in the spring because the Department of Justice released its Statement of Expenditures for the special counsel's office. From May 17, 2017, through March 31, 2018, the investigation cost about $16.7 million.

An updated report detailing Mueller's costs is expected soon.

But it's unlikely that those costs will exceed the amount to be seized from Manafort.

The White House did not immediately respond to a request for comment.

-- CNBC's Dan Mangan contributed to this report.