If your veterinarian is unable or unwilling to treat feline mange, or is unsuccessful after one month of treatment, please see If Your Veterinarian Can't Help.
If we could have stuffed Bandit into a cat carrier and taken him to the vet, this would be a very short story, with a happy ending very soon thereafter.
Unfortunately, Bandit is essentially feral. He is a neighborhood stray, and he usually doesn't let people get close to him. Since my wife and I are nonthreatening, gentle, and offer him food, he sometimes lets us come near.
When we tried to get him into the cat carrier, he fought back, scratched us up, and escaped. And he wouldn't let us come near him for a week. As a result, I was reduced to the desperate measure of a home mange cure in order to save his life.
Your first choice should be a trip to the veterinarian.