Tame feral street cat in need of vet

I have a street cat that lives in my front yard over the last few weeks he began to develop sores on him and now I'm seeing hair begin to start missing from his ears. He's neutered and his ear is clipped from the neutering. Does anyone know where I can take him and get him a cheap prescription for what I think might be mange? It's rapidly spread the last few weeks and really want to help him! Ps: For anyone wondering why I won't take captain murder mittens inside my house, I have 4 frogs and three house roaming rabbits. As much as I love him he's not my cat but I'm interested in keeping him safe 10 pet photos for the animal tax. Thank you for all your help!. Mom to three kids and 9 animals...