You can use a home remedy in this. If you can see the infection, warm compression several times a day will be of help. You can also use cod liver oil or vitamin oil, apple cider vinegar, macerated garlic or herbal flea powder. Ensure the infection does not run dry of any of what you will choose.
Go to your local ASPCA Or Humane Society. They will treat him on a sliding-scale, ability-to-pay basis. I've done this myself, and my cat received kind, gentle, thorough and effective treatment, and they were polite to me as well. They're good people.