One Louisiana company makes prototypes, another can fabricate metal, while yet another moves earth. Each wants in as subcontractors on the proposed multibillion-dollar border wall along the U.S. boundary with Mexico.

An internal report prepared for Homeland Security Secretary John Kelly estimated that a wall along the entire border would cost about $21 billion. Congressional Republicans have estimated a more moderate price tag of $12 billion to $15 billion.

“We’re just looking to learn what the opportunity is,” said Brandon Iglesias, founder of ReactWell LLC, a New Orleans-based science, engineering and technology company.

James Larry Prudhomme II, owner and president of J&L Investments of Natchitoches LLC, said his Baton Rouge company, which has 13 employees, could play a role in any of the earthworks involved in building the wall, as well as erecting the structure. “A big project like this, we would like to be a part of it,” he said.

Customs and Border Protection, the Homeland Security agency that will eventually patrol and maintain any new fencing or walls, has asked contractors to submit proposals for a 30-foot-high wall that is difficult to climb or cut through. Bids were originally due to the government last week, but the deadline was extended to Tuesday amid questions from possible bidders.

In a pair of contract notices made public two weeks ago, the government said proposals could lay out plans for a solid concrete wall or a structure that can be seen through by border agents. As of last week, 730 businesses had signed on to a presolicitation notice posted on the Federal Business Opportunities website, indicating that they are interested in being vendors for the construction of the wall. Seven of the companies indicating interest are from Louisiana.

The other Louisiana companies that filled out forms on the website as of last week were Macro Companies Inc. of Broussard; American Integration Contractors LLC of Lafayette; Alfred Miller Contracting Co. of Lake Charles; Cajun Constructors LLC of Baton Rouge; and Highly Favored Home Inspection LLC in Port Allen.

“We haven’t submitted a bid, we’re just listening,” said Iglesias, of ReactWell, which was founded in 2012. It makes prototypes for a variety of industries, including renewable energy, defense, aerospace, and oil and gas.

While Trump’s plans for a border wall have generated controversy, Chuck Edwards, of Highly Favored Home Inspection LLC in Port Allen, said he’s not concerned about any backlash. “Business is business,” he said. “I don’t play with politically correct people. They don’t mean nothing to me.”

Edwards started the home inspection business about 15 years ago. In the past year, he expanded the business to build custom gates and metal fabrication. He’s hoping his company, which includes two part-time workers, could play a role as a subcontractor handling metal fabrication for the massive border wall. “Whoever gets awarded a contract will need some help,” he said.

However, building the wall faces hurdles, both political and physical.

Geographic and physical challenges — including the Rio Grande and threatened wildlife — will make it difficult to build the "big, beautiful wall" that President Donald Trump has promised on the U.S.-Mexico border, Interior Secretary Ryan Zinke said Wednesday.

Building a wall "is complex in some areas," including Big Bend National Park and along the river, which twists through nearly half of the 2,000-mile border, Zinke said.

Hundreds of species live within 30 miles of the border, including threatened jaguars and Mexican gray wolves. The Trump administration is poised to relax protections for the jaguars, which live in northern Mexico and parts of the southwestern United States, to make it easier to build the wall.

Throughout the campaign, Trump energized his crowds with his insistence that a wall will be constructed along the border and that Mexico will pay for it. Zinke's comments, and the administration's budget proposal seeking billions in U.S. taxpayer dollars to finance the project, offer a reality check and a possible sign the president is moving away from his initial plan.

The Department of Homeland Security is responsible for the border wall, but Zinke said the Interior Department will play a critical support role.

"At the end of the day, what's important is American security and to make sure we have a border," Zinke told reporters on a conference call. "Without a border, a nation cannot exist."

Homeland's Kelly told Congress in January that a wall wouldn't be a complete fix for the border.

"A physical barrier in and of itself will not do the job," Kelly said during his confirmation hearing. "Certainly it has to be a layered approach."

Zinke's comments appeared to bolster that view and followed remarks he made last week to the Public Lands Council, a group that represents Western ranchers.

"The border is complicated, as far as building a physical wall," Zinke said in remarks first reported by E&E News. "The Rio Grande, what side of the river are you going to put the wall? We're not going to put it on our side and cede the river to Mexico. And we're probably not going to put it in the middle of the river."

Electronic monitors may be more appropriate in that region, Zinke said, while areas with imposing natural features may not require additional reinforcements.

The border is already dotted with underground sensors and camera towers, along with about 700 miles of fencing in Texas, New Mexico, Arizona and California, and it's unclear how much new fencing the Trump administration is proposing.

According to new budget details sent to Congress, the administration wants immediate funding to complete an existing barrier in the Rio Grande Valley, $500 million to complete 28 miles of a border levee wall near McAllen, Texas, and $350 million for construction along two segments near San Diego.

Senate Democrats have threatened to filibuster any provision providing money for the wall. Many Republicans aren't very enthusiastic about the plan and say the White House has given them few specifics.

Republican Missouri Sen. Roy Blunt, a key budget negotiator, said the Senate is unlikely to include money for a border wall in a broader spending package to avert a partial government shutdown this month.

Fencing that is already in place is a mixture of various designs, including towering steel bollards designed to keep both people and vehicles from moving north and shorter steel posts aimed only at blocking cars. In parts of Texas' Rio Grande Valley, some stretches of fencing are nearly a mile away from the border in part to accommodate flood plains and an international treaty.

And in Texas, almost all of the land along the border is privately owned. When former President George W. Bush tried to build border fencing starting in 2006, he faced stiff opposition from local ranchers and farmers, many of whom took the government to court on plans to use their land.

Advocate business writer Timothy Boone and Associated Press writers Matthew Daly and Alicia A. Caldwell contributed to this report.