sorry, moondog
influenced by my Arts background there 
I did think your surprise at £2k for 4 visits was odd, tbh - I am assuming that phlebas was talkking about consultant visits.
dd1 currently has SI, not AIT. still wishy-washy in terms of evidence, yes I know. But tbh, I don't rule anything out.
we took her to the OT for assessment prior to tribunal - he also does the SI (looks like a lot of jumping around at soft play, and being hurled around on swings to me!). we decided, following that, to give it a go, and see. during the session, he also works on more conventional OT stuff (fine motor skills, etc) so we knew at a minimum dd1 would be gaining skills there.
following dd1's first session (first "proper" session, post assessment), we found the following:
dd1 (next day) walked around a shopping centre (a new one, so unfamiliar environment), whereas previously she would have galloped/whooped/shouted ehr way around.
she listened when we asked her to wait, and followed (basic) directions as to where we were going next (eg "going into the nappy shop now (Boots)" or "need to go downstairs to the supermarket")
she also listened when we asked her to mind out for other shoppers walking too. she didn't always move out of the way, but she did take note, and stand still so they could pass her safely.
she was able to listen when we told her we would not go on the escalator (phobic), and instead of shrieking and hurling herself to the floor, she managed to walk past it (albeit with fingers in ears, repeating "it's ok, it's ok") - I would previously have had to carry her past (and even then she protested)
the list goes on, tbh.
we were absolutely gobsmacked.
all anecdotal, of course, but it'll do us, and meant we were convinced enough to give it a good 6 months or so (not on a sign up or anyhting, but thought it good enough results after 1 session to give it a fair run)