Can a cat with (possible) mange be treated without a vet?

We have a large feral cat population in my neighborhood, and my neighbors have been caring for one of the friendliest cats for the last year or so.
They have two indoor cats of their own, so the stray isn’t permitted in the house, but they put out food and water and they built a very nice shelter for the cat to use over the winter.

Now, my neighbor had called me because she said the cat was injured and she thought it had been attacked. I took a look at the cat and it looks like mange, to me, not an injury. I know that mange isn’t extremely common in cats, but he is missing large patches of fur on the neck and head and has scaly, scabby skin on its neck and ears and it is always scratching. I didn’t see any sign of fleas.

Is there anything that they can do for the cat? It’s very friendly, it was definitely a pet at some point, so approaching and touching the cat isn’t an issue.