Thanks everyone - I have alot of helpful stuff to go through here. It DOES seem there is a better solution to the $20/month thing, so even though I am usually reluctant to post here when I struggle to understand the answers, I am still far better off doing so.
I will heed the heads-up on Vodafone.
I have been with Woosh since they started and although I have always found their customer service excellent, we have never used more than 10,000MB/month and we pay them $55 for 55,000MB and then about $55 to Spark for the homeline .... which seems very old school now even to me and I thought it was time I got a grip and changed to a package deal for about $75 or thereabouts. We are limited in which plan we can have with Woosh because we are rural (can only have standard broadband, not air or anything fast

I'm surprised the security alarm guy couldn't have told me some of this.
To be honest I don't really understand the DNS side of it fully yet, but I'm working on it. I'm trying to figure out where I start. Am I right in thinking it all comes down to my router whether I can do the dynamic DNS? or is it the camera DVR as well? Probably just as well I am finding all this out before we actually have it done - I can change anything at this point. I have googled the DVR he has quoted us for, but I don't know what I am looking for in the specs. Similarly, would I not just be better off buying a new router - if I find my current one is not suitable - and saving the monthly fee, if I can then do it for free? Or am I misunderstanding this?
Thanks again.