Questions About Natural Treatments for Autism

I don't want to sound like skeptic, but before throwing my son into any treatment and throwing money into that treatment, I really would like some questions answered first.

From what I have read, it seems that many children who have an ASD (Autistic Spectrum Disorder) are also plagued by other health issues such as digestion and bowel problems. There is a theory that vaccination shots are associated with the onset of autism, and it's the mercury in the vaccines that cause the neurological problem. As well, there is the environment factor: there are many toxins around and within us. For children with autism, it is theorised that these toxins must be purged from their system so that they can absorb the treatment (speech therapy, behavioural therapy) that they need.

I don't think that Little R has any digestion or immune system issues. I think that he is a healthy little preschooler who has difficulty using language and lives in his own little world. However, could be wrong.

First question: how do I find out (preferably without paying out a lot of money) if he has allergies, in tolerances, imbalances, toxin overload, etc.? If Little R indeed has a digestion problem, would it subtle enough for us not to notice?

Second question: for the children that were helped by biomedical treatment, were these children physically ill to begin with? Did they suffer from seizures? Did they all have obvious digestion problems?

Third question: out of the children who have tried biomedical treatment, what percentage saw significant improvement or even full recovery? How long does it take?

Fourth question: how much would a children need to see the biomedical professional before progress is seen? how much would a family need to pay to have a child recovered? This includes the fee for consultation, purchasing of vitamins/supplements, special food (like gluten and yeast free)?

Fifth question: do any of the testing or applications of the biomedical treatment have any risks or side-effects?

Sixth question: how does behavioural therapy fit into biomedical treatment?

So, I'm concerned with: which group of ASD children benefits from biomedical treatment? is it safe? How much am I looking to spend? How do I know my child will benefit from such a treatment?