OK. So there are lots of "homemade" treatments that simply don't do anything. At one time this was treated with lime dips mixed with borax which was done daily, took 6-8 weeks, and the animal has to be restrained in an e-collar the entire time because licking their fur will poison them. Not an option. Don't use the neem oil either.
So we are left with the Revolution or ivermectin.
Mange infects dogs and cats too, and I found a site -
https://www.animalsos-sl.org/product...nge-ear-mites/ - where they are soliciting donations to treat the street dogs that are infested with mange. The product they use is called "Advocate" which is the name that a US drug, named "Advantage" is sold as. It can also be used to treat mange. I don't know the cost if you just purchase it off the shelf, but perhaps, perhaps, if you contacted this charity, and offered to give a donation in exchange for just ONE of the little vials of the med they might help you out.
If you can get some coconut oil, rubbing it on the skin where it is red and rough may soothe it some. IT WILL NOT KILL THE MITES. They are not on the skin surface so you can't wash them off or smear anything on their skin to kill them. The treatments all work internally.
It is possible that this is a fungal infection of some kind, but your description of "silver dust" made me sit up straight because that is exactly what the loosened skin flakes look like. Our gray squirrels tend to start showing signs on their ears first because the fur is so thin there, and the ears crinkle up and look like someone dusted them with silver eyeshadow. I have never seen this on one that did not have mange...