Depending where you live EHCPs don't necessarily come with additional funding
By law, EHCPs always come with additional funding if that is what is required. Some local authorities like to make out that that is not the case, but it is utter nonsense. Provided section F of the EHCP properly specifies the provision the child needs, the council has to ensure that they receive it, otherwise they can be taken to court using legal aid in the child's name.
I would really be quite worried about a SENCO who seriously comes out with a statement that they have other children with autism without EHCPs therefore your child shouldn't have one. It's just basic that autism is a spectrum, and may manifest in one child totally differently from the way it does in another.
The legal criteria for the first stage in the process, asking for assessment, are simply that your child has or may have SEN, and that he may need help through an EHC Plan. So far as the second part of that test goes, you need to look at things like evidence of progress (including non-academic progress, e.g. communication, anxiety, sensory problems etc) and, in particular, whether the child's needs can be met within the resources normally available in mainstream schools.
You can ask for an EHC needs assessment yourself - www.ipsea.org.uk/asking-for-an-ehc-needs-assessment. If the school doesn't support you, the council will probably refuse, but it is quite easy to appeal and appeals have a success rate in the region of 90%.