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Often the discharge from the eyes starts out clear but dries that dark brown/black color. Usually bacterial infections cause cloudy yellow or green discharge. Since both his eyes and nose are affected, I wonder if he might have a feline herpesvirus infection.
There is nothing to kill a virus itself (just as a cold needs to run its course), but there are some things to try to make him feel better. You can sit in a steamy bathroom with him to help clear his respiratory secretions.
If he stops eating, you can add warm water to his food, try canned cat food, tuna fish, or meat baby food. Also heat it up slightly to increase the stinkiness. (When they get stuffed up and can't smell, they lose their appetites).
Last, you can purchase an L-lysine supplement for him. This supplement stops the virus from replicating, and gives his immune system a chance to get rid of the problem. These supplements can be found on the internet, such as Enisyl or Viralys.
From what you are describing, his condition sounds consistent with something called stomatitis. This is related to an over reaction by his immune system to the bacteria in his mouth. It causes severe inflammation of the gums, very bad breath, difficulty eating and often weight loss.
Unfortunately, the treatment for this is usually extraction of the majority of his teeth. I do have a couple of patients who are doing okay with medical therapy (antibiotics and intensive home dental care), but this is not usually successful. At this point, his mouth would be too painful to begin a home care regime.
Since finances are an issue, perhaps you could have him seen at the local Humane Society or SPCA just to have the diagnosis confirmed. At that point you can evaluate your options for him.
Good luck and Merry Christmas.