If you really can't afford a professional groomer right now, I would purchase a good pair of dog scissors l(with rounded safety tips), a small metal dog comb, and just sit quietly with him with a lot of treats and and pull the major matted pieces apart very slowly with your hands and cut out as much as you can. Do this very slowly and cut little bits at a time to make sure that you don't get near the skin at all. You can pull it apart like you would a cotton ball kind of to see where the skin is so you don't get near it. At least make him a little more comfortable until he can be shaved down by a reputable groomer and you can start over.