I understand that your fellow is uncomfortable due to an ear infection despite your attempts to treat it.
Ear mites in an adult dog are very uncommon, and the topical drugs that stores sell to treat mites are very, very irritating to the ear so I am not surprised his ear is getting raw.
Of course the ideal situation is to see a veterinarian and have his ear debris tested to see what sort of infection he has to get him on the right medication, but I understand that is a struggle given your finances.
In general systemic oral antibiotics will not successfully treat an ear infection in a dog. Unlike people that get inner ear infections dog ear infections are in the outer ear canal, and systemic antibiotics don't penetrate the skin of the ear and waxy debris in the ear well at all, so they don't work very well unless the infection spreads to the inner ear. If the infection spreads to the inner ear we can add systemic antibiotics, although SMZ would not necessarily be one we would use because it has a limited spectrum of efficacy against bacteria that normally cause inner ear infections in dogs and it is more likely to cause side effects. Even if we use systemic antibiotics we would still need to use topical medication.
There are some other systemic medications that can help prevent some of the predisposing factors for developing infections, and thus are useful for prevention, but it is extremely rare to be able to give an oral medication, especially an antibiotic, and cure an ear infection.
In some less common types of ear infection with very aggressive bacteria (pseudomonas for example) that cause erosions of the ear canal skin we may need to combine oral systemic antibiotics with topical medications too. That isn't the usual though.
While he does need to see his veterinarian in the meantime there are some things that we can do to help him feel more comfortable.
Since most ear infections are secondary to allergies and the inflammation they cause you can use a combination of antihistamines and high doses of omega-3 fatty acids to help with those. In combination fatty acids and antihistamines work synergistically, much better than either one alone.
You can try:
1)Benadryl (diphenhydramine only don't use the combination products with decongestants or acetaminophen as they can be toxic) at a dose of 1mg to 2mg per pound or one 25mg capsule per 15 to 25 pounds of body weight orally every 8 hours.
OR 2)Claritin (loratidine) at 5mg per 25 pounds of body weight once or twice daily.
OR 3)Hydroxyzine at 1mg per pound of body weight orally every 8 hours.
OR 4) Chlorpheniramine at 4mg to 8mg per dog once or twice daily.
OR 5) Zyrtec (Cetirizine hydrochloride) at 1/2 mg per pound of body weight orally every 24 hours. That would be one 10mg tablet per 20 pounds of body weight. Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because dogs cannot tolerate decongestants.
Some dogs do better on one antihistamine rather than another. Give the one you pick a week trial and if it isn't working to reduce itchiness try another. Be aware that antihistamines can cause sleepiness or hyperactivity in some dogs. These side effects do wear off with repeated use.
Omega-3 fatty acids are fish oil products. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your pup's weight. I recommend an omega 3 fatty acid dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give him 20mgs of EPA per pound of body weight per day. For example an 85 pound dog could take 1700mg of EPA per day.
I also recommend using a gentle ear cleaner like Oticlens daily now to remove as much of the waxy debris as possible. This removes excess wax and keeps the ear pH at levels that discourage infections. When the ear is sore many dogs won't let you squirt things in their ear but if you soak a cotton ball with the cleaner, then place it at the top of the ear canal and massage the ear from the outside, putting pressure on the soaked cotton ball, the cleaner will be instilled easily. Wipe out excess cleaner and waxy debris with dry cotton balls.
Once you have his infection treated and cleared use the cleaner twice a week as that helps prevent infections and also allows you to know what a normal ear looks like and catch ear infections very early.
Sometimes with an early infection simply cleaning the ear daily is enough to stop it in its tracks. I don't believe that is the case with him now, but may help in the future.
If his ear canal skin surface is very red after cleaning you can apply a light coat of cortisone cream (like cortaid) to the ear skin with a cotton ball.
Then I recommend that he see a veterinarian as soon as possible.
If your regular veterinarian is beyond your means financially now your other option is to contact your local shelter or humane society and see if they run a low cost clinic or know of one in your area.
If not here is a web-page that lists some that may be able to help:
Other sources of help can be found here: http://speakingforspot.com/?p=Financial%20Assistance%20for%20Veterinary%20Care
Do not clean his ear the day of his veterinary appointment so they can gather a sample of the wax for testing.
I also want to add that if your fellow has had repeated ear infections there is likely some sort of predisposing factor. In most cases it is allergic inflammation, particularly food allergies, so you might want to discuss feeding him a prescription hypoallergenic diet with his veterinarian. I recommend Hills z/d, Purina Pro Plan Veterinary diets HA or Royal Canin restricted protein diets.
Best of luck with your fellow, please let me know if you have any further questions.