The Hanen training itself is run by SLTs for SLTs, so it's not possible to join one of their training courses (the expensive ones you mention - yes they are expensive but the cost is met by the SLT's employer) unless you are a practicing SLT.
The idea is that the SLT then rolls out the training locally. I'm a Hanen-trained SLT and I can recommend it, but it isn't provided in every area.
Ideally it ought to be run as a group, but the members of the group all have to have children at similar levels of development. It can be hard to organise this. In practice I have used Hanen principles and workbooks to see parents on an individual basis and used videotape as the Hanen programme requires.
It does take a bit of commitment from the parents, and I think you really lack the support of a group if you are being seen individually, but it's great, and the book mentioned provides good ideas.
The best thing about it is the video tape. Once you get over the self-conciousness, it's a great way to check whether you are getting it right.