There are several ways to treat mange. If this is demodectic mange (non contagious) you can read about how to cope with it here
www.marvistavet.com/html/body_demodectic_mange.html
If its sarcoptic or contagious mange you can read about it here
www.marvistavet.com/html/sarcoptic_mange.html
Ivermectin is pretty inexpensive to use and I think the vet may have been quoting you prices to use Milbemycin on this size dog.
If Ivermectin is not contraindicated in OES then you might consider that.
Even though demodex can resolve on its own most vets advise treatment to speed recovery and to keep the dog more comfortable.
Your home remedy is both toxic and dangerous.
http://www.petcaretips.net/pet_poisoning.html
Better to use a known chemical that actually works and has a known dosage amount etc.
Hope this helps you!
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