Adopted mustangs have current vaccinations, Ms. Santagata said, but annual veterinary care could cost about $300 “if there are no problems.” About $50 every eight to 10 weeks goes toward having their hooves professionally trimmed. Many owners just feed their mustangs hay, similar to their diet on the open range, rather than more expensive grain with the hay, she said.

“They are so hardy,” Ms. Santagata said. “They are built to survive.”

Other costs include adapting corrals with six-foot-high paneled fencing so the wild horses cannot escape, and providing them with open-sided sheds that they can enter themselves when they need shelter, because they are not easily led.

The most expensive part of owning a wild horse, Ms. Santagata said, is paying for experienced trainers. At 41, she has been around horses all her life, but she said she could handle only basic “gentling” of a wild mustang. When the horses are in her corrals, she uses a soft opening, by approaching and retreating, so they get accustomed to her.

“You walk around it and see how it reacts to you,” she said. “I have had mustangs that would not look at me for months.”

She gradually introduces them to halters and to being led around, which she is able to accomplish in about three months, she said. For advanced skills like riding, she sends the mustangs to professionals, but not before she has grown to know them.

“I look at them like I am adopting a living legend,” Ms. Santagata said. “They are a mystical creature out in the wild, and only a few lucky ones can find them.”