While Donald Trump doubled down this week on his vow to make Mexico pay for his proposed southern border wall, his campaign is reported to be weighing options that don’t necessarily involve the seemingly far-fetched scenario of the Mexican government handing America a great, big check.

LifeZette first reported that the Republican presidential nominee and his top advisers are looking at using assets seized from drug cartels and other traffickers. This reportedly could involve establishing a “joint border security fund” -- holding seized assets from crackdowns on both sides of the border – for border construction and maintenance.

Trump, asked Thursday by Fox News about the report, did not deny the option is on the table.

“There are many ways that they can pay for the wall,” Trump said, calling it a “negotiation.”

But he again insisted, “The United States will not be paying for the wall. Mexico will be paying for the wall.”

Breitbart News, whose chairman Stephen Bannon left to be Trump’s campaign CEO, also reported that cartel resources would be seized to fund the wall if Trump wins.

Trump supporter, and former presidential primary rival, Ben Carson floated another option Thursday night.

Speaking with Fox News, Carson said money saved from enforcing the border could be used – though he did not elaborate on what level of savings the federal government could expect, particularly when Trump is proposing spending more money on border security resources.

“Recognize that a lot of money is going to be saved by enforcing our borders, by not, you know, giving various types of benefits to people who are here illegally,” Carson said. “That money is money that we otherwise would not have had and that can be applied to the wall and various other things. That’s I believe the spirit in which that comment is made. I don't think Mexico is going to write a check out and say here, pay for the wall.”

Trump has not addressed such details on the stump.

He declared in his immigration policy speech Wednesday night that, “Mexico will pay for the wall … they don’t know it yet, but they’re going to pay.”

That came after Trump met with Mexican President Enrique Pena Nieto in Mexico City, and both men left the meeting battling over the payment issue. Trump said they didn’t discuss “payment,” while Pena Nieto said he made clear Mexico will not put up the money.

According to The Wall Street Journal, Trump added the line about payment into his Phoenix speech, in response to Pena Nieto’s claims.

If a Trump administration did pursue using cartel assets to fund a wall, it would take billions. Trump has estimated the wall could be built for as little as $8 billion, though other analyses have put the cost much higher.

Estimates of Mexican cartel revenue vary drastically. The U.S. government estimated a decade ago that Mexican traffickers make nearly $14 billion on drug sales to the U.S.