“buying all of the private land along the US/Mexico border could probably get pretty pricey”
The Government just needs a 150 foot wide strip, which adds up to about 18 acres per mile.
The 750 miles along California, Arizona and New Mexico is overwhelmingly Government owned, and the Roosevelt Reservation (first 60 feet) is already in effect.
The total plan submitted to Congress last year called for a total of 1,100 miles of barrier. All things considered, the minimum required would be about 10,000 acres, averaging a few thousand per acre - a few tens of millions of dollars worth of real estate. Significant settlement costs will also be needed to buy out landowners completely in many cases, so $100-200 million is a ballpark estimate.
Laredo is also angling to get a waterfront development project thrown in as a sweetener, so maybe another $50-100 million if they get a really sweet payoff. The 2019 appropriation included a requirement to come to agreement with about a half dozen local Governments on the barrier route, and being able to negotiate some such upgrades is likely a big reason for that provision.
In rural areas of farmland and ranches, the land is relatively inexpensive, and if good accommodation is made for water needs, local owners often welcome good barrier.
The Rio Grande Valley and the border cities - especially Laredo - is where the land acquisition is most difficult and expensive. The Trump Administration proposes to do all of that with the money it has identified for this year.
As luck would have it, the guy leading the effort happens to be a world class real estate developer, with extensive experience in eminent domain issues. We can be reasonably sure that he has required the program to shown him a realistic plan for managing the land acquisition. But the bottom line is that neither land acquisition costs, nor the legal aspects of exercising eminent domain, are showstoppers - just normal parts of Government construction projects.
Good I formation! Thanks!!