I saw great improvement within 24 hours, but it took about a month to totally clear up.
Milk of Magnesia
This post has been a Godsend for my Border Collie mix. He suffered with a bacterial/yeast infection that started at the base of his tail and spread like wildfire the entire length of his underbelly, including his legs, to his chin. He lost all his hair and had red/gray elephant skin. Went down the same road you did and probably tried all the remedies you did, plus the drug ketaconozole, which cleared it up in 2 weeks, but it came back and the second round did nothing (already resistant! ). Three years and 4 vets later, I saw this post. I started applying the MOM topically and saw immediate improvement, and in just 2-3 months it was all gone, except for one little stubborn spot on his chest, which would have probably been gone long ago had I not become less diligent about applying the MOM. One year later he is still infection free and his beautiful long blonde coat has grown back in and his skin is pink, which I thought would never be normal again. I thought it had something to do with changing the ph environment to something the yeast could not survive in. Whatever it was, it's unbelievable that I, like you, spent lots of money and ended up resolving it for cheap, cheap, cheap!
Milk of Magnesia
My poor golden retriever/ basset hound mix had the worst case of incurable yeast in his ears I have ever saw and I have owned many many dogs. Oddly, I saw a drag queen say that milk of magnesia, topically, would prevent sweating under makeup for shows with hard hot lighting.
Siwwy had been given every prescription anti yeast medication, every vinegar drop method, every borax based method, all manners of homeopathic cures and things that cost so much money I was wondering if I would go broke. And all of the doctors antibiotics and creams to cure the secondary infections.
As yeast depends on moisture, I decided to go there with MOM. I painted it on rubbed it in, held him until it dried and in a month his ears were completely healed and no scars even remain. Thanks RuPauls Drag Race my dog loves a drag queen now! This is no joke, try it it works!