Hi.
I can't help you on the ABA front... But if its something you feel would work for your son, you need to look into it, and just because your LEA hasn't funded it before doesn't mean they never will!
I'm not in kent I'm afraid, but my son is a couple of months older then your ds, and wanted ot say, that whilst it doesn't seem much, him learning to exchange PECS is an acheivement.
What other methods are you using with him?
We borrowed a VHS copy of 'more then words' from our SALT, and have since bought the book from Winslow as whilst its comon sense its handy ot have a reference point... and honestly, that has beenthe most helpful thing we've accessed with a view to helping our son.. It describe how to make opportunities for comuncation, it almost teaches the child to be motivated if that makes sense, and it also identifies the different stages of communication so you can gear your approach appropriatley.
We currently use Makaton signs alongside very basic simplified language when talking to our son, and are moving onto PECS symbols instead of photos or the more lexical Makaton symbols, and after a year of signing to our son, he has in the past few weeks started to make sense of it, and he's started echoing speach and even uses 3 words and signs together properly, his SALT was in raptures about that, telling us how brilliant nad amazig this acheivement is... which it is, but 'aeroplane, rainbow and zebra' are not gong to get him very far in life... what I'm trying to say is whilst you feel like your losing them, and nothings working, they are taking things in and what seems like a ridiculous pointless exercise does pay off in the end...
Most likely someone wil have posted soemthing more relevent and helpful in the time I took to type that!
I have waffled a lot, sorry.
take care
emma x