What is the best treatment for Demodex Canis or Demodex Mange?

We're from Pasig City Philippines, we wish someone or an individual from same place help us solving our problem with our Shitzu dog. He is already 20 months old or 5 months old (4 kgs) and he was diagnosed having a generalized Demodex Canis. The veterinarian advised us that he will be treated by bathing them with a specialized medicine for this case but we can't afford the expensive treatment for it will last for months. I am looking for inexpensive way to solve our problem and we are very much worried for our dog. He is not well this time for spending most of his time scratching itch of this culprit. Hope someone will give a best information... thanks