I have a 2 feral cats. One hides 99% of the time. Stealing cat food and water I put out daily at night. The other resides in the barn preferring the overhead 2x6 walkways and loft areas. Sleeping in the cat boxes and blankets I put on top of the 6' tall shelves. She shows up when I call for the AM feeding making biscuits when I'm bringing food but forbids me to touch her. It's been 4 yrs of this behavior. I just accept the no contact rule and appreciate the rodent duty they have do, having eliminated the unwanted critters that used to eat our car wiring harnesses and build nests in idle equipment.
Feral cats are trapped by the ASPCA. Neutered, vaccinated, chipped and ear tipped for easy ID. My cost is just dry cat food and treats.
We took 4 to get 2 that stayed. They said 50% success was typical. I'd do it again if needed. Otherwise these cats have a very low chance of survival.