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President Donald Trump’s proposed border wall has the serious attention of more than 300 contractors, including one from Wisconsin.

Michels Corp., of Brownsville, is on the list of firms that have so far expressed interest in a solicitation for preliminary work for the wall that the president has promised to have built along the 2,000-mile border between the U.S. and Mexico.

Hundreds of companies, Michels Corp. included, were named on a list of interested vendors sent out by the office of U.S. Customs and Border Protection earlier this year. By Thursday, the list of vendors had reached 333.

The presolicitation, which can be found on the Federal Business Opportunities website, seeks conceptual designs and prototypes showing what the wall might look like.

David Stegeman, chief legal officer of Michels Corp., declined on Thursday to comment on the company’s interest in building the border wall.

Were Michels Corp. chosen for the project, it wouldn’t be the first time the Wisconsin-based contractor has ventured into the southern U.S. The firm recently performed horizontal drilling and pipeline installation work in Texas and also has an office in Houston.

The office of U.S. Customs and Border Protection’s posting states that bids will be sought for the border wall on or around Monday. Respondents will be required to submit a “concept paper” showing prototypes by Friday, March 10. Following a quick evaluation, the agency will have the field of candidates narrowed by March 20. The finalists will need to submit offers with their proposed costs by March 24.

A Customs and Border Protection spokesman said in an email that the purpose of the solicitation is to develop design standards for a border wall meant to further deter illegal entry into the country. The design and construction of the project are both to be expedited.

Prototyping is a common way to decide how best to design a structure such as the proposed border wall, said the spokesman.

“Through the construction of prototypes, CBP will partner with industry to identify the best means and methods to construct (the) border wall before making a more substantial investment in construction,” he said.

The agency’s notice gave no details concerning where the wall would be built first and how many miles would be covered initially.

Speaking recently to the audience at the Conservative Political Action Conference, Trump said the project’s construction will start “very soon” and is “way, way, way ahead of schedule.”

One big obstacle standing in the way of the project, perhaps the biggest one, is money. Any funding for the project will have to come from Congress. And lawmakers have so far given little indication of when they might take up such a spending measure. What’s more, uncertainty continues to hang over the question of exactly how much the project will cost.

The Government Accountability Office has estimated that fencing meant to prevent immigrants from entering the country on foot would cost $6.5 million. Vehicle barriers would cost $1.8 million a mile. Republican leaders in Congress have estimated the total cost of Trump’s wall proposal at between $12 billion and $15 billion. Trump himself has suggested $12 billion.

Other sources have suggested a much higher figure, though. A separate report from the Homeland Security Department has estimated the cost at about $21 billion, according to a U.S. government official who is involved in border issues. The official spoke on condition of anonymity because the report has not been made public.

Associated Press writers Elliot Spagat and Alicia A. Caldwell also contributed to this report.