Hi Keith
There is probably a large difference between "printing" and "publishing". If you put the book together yourself and get the book printed as an A5/A4 book, it would be relatively inexpensive - you are the publisher. Printers can assist with the design and layout, but usually have no input as to the content.
My advice for the above would be talk to a local printer before designing & setting up the book. The size of margins, for example, can be critical to the type of binding (as I found out too late & had to reset much of my book). Colour, is, of course much more expensive to print than black/white. If you sequence pages correctly you can reduce the number of pages that need colour, thus reducing cost. Offset printing costs per copy (as opposed to photocopy or "print on demand") reduce significantly with volume.
If, however, you want to have the book designed & edited etc etc, you either have to pay to have this done (plus pay for printing) unless there is such content that a publisher would see it as financially viable to produce.
Like others have said, I have started with loose leaf booklets, as the content is still changing, but I have turned one section into a bound booklet as I think (and hope) I have it correct.
Trish