Hey OP... What behaviours is your son displaying ??
I don't know about Brainwave but I'm reluctant to suggest getting independent reports unless it's for education purposes ( seeking EHCPs) diagnosis's or if the assessment is needed to do follow up therapy.
The ICAN Meath school offer a free SLT and an educational assessment for parents who are on low income... though I'm not sure if it's for parents who are looking for a place at the school in order to get an assessment. I'm not sure, call and ask.
I will apply for an EHCP... when DS was younger.. sites like "teachmetotalk" was very helpful... the Outofsync child is a good book to read.
You can speak to your nearest sure start centre and ask if they run behaviour courses... the most common is triple P... some parents have not found this helpful for their ASD children but for me it helped to focus on DS positive behaviours.
When DS was going through a really bad stage... I created a visual timetable of what I want him to do " Sit nicely, talk quietly (not shouting).... etc etc.
I find when DS was that age who has and still has social/speech language and communication difficulties is mainly to due with the frustration of not being able to communicate and amongst other things. My DS is very good at labelling feelings and can easily identify emotions but he has trouble expressing this himself. So when he felt overwhelmed... I hoped he would eventually tell me " mum, I need a break" "Mum, I feel sad because....". What helped was reading stories to him... I'll ask him " how does that character feel... or why is he upset". This helped DS relate his emotions to the characters in the book... so now, DS can say things like " I feel upset" without going into a huge meltdown.
The book "Hansen more than words" is good also.