U.S. Customs and Border Protection, which oversees the Border Patrol, said in a statement that ATEP has disrupted smuggling networks and contributed to an overall decline in recidivism rates. The program, it said, "was designed specifically to create displacement and increase time between entry attempts."
Asked to provide the cost, Customs and Border Protection said ATEP "uses resources that were already in place ... and cannot be separated from the normal cost of doing business."
Until last year, ICE typically paid a night of detention, which cost an average of $119 a person.
Air-conditioned buses still leave the Border Patrol's Tucson compound each weekday with up to 188 passengers. Two follow a 700-mile route east to Del Rio, Texas, where they are dropped off in the neighboring Mexican city of Ciudad Acuna. Two head about 300 miles west toward Mexicali.
As ATEP grew, Mexicali became the top destination for those deported to Mexico, peaking at 66,517 in 2012, a 24 percent increase from two years earlier, according to Mexico's National Immigration Institute. Several migrant shelters opened in the sprawling city of 750,000 to handle the influx.
Migrants gravitate to a breezy, sunlit hallway to discuss their next moves at the Hotel of the Deported Migrant, which housed up to 300 people a night after opening in 2010. The Mexican government offers discounted bus tickets and a limited number of free flights to their hometowns, but few consider it.
Abel Delgado, who lived in the Phoenix area for 23 years and was a cook and construction worker before he was deported in 2010, was bused from Tucson after four days of walking through the Arizona desert.
The 30-year-old planned to reunite with his smuggler for another attempt in Arizona after the summer heat, determined to rejoin his wife and daughters, ages 5 and 8.
"If I didn't have family, I'd stay here," he said.