In reply to GarethSL:
I've written about 25 guidebooks so -
I'm not sure how big your book is going to be, but don't underestimate the time is takes to do the layout/text. I have always reckoned (when working more or less full-time on a book) to get a single page a day done.
I have a really bad habit of leaving the jobs I don't like (maps, local info, introductions etc) until the end, which is a poor idea 'cos it means the final stages of the book becomes a chore.
I don't know how you can contemplate doing a book without a proper publishing package - we use Adobe InDesign, which is superb, but it costs and there is a learning curve associated with it.
Adverts are a fair idea, they offset the print costs and can be useful freebies for people/organisations etc who have helped.
Most important - double check all your info, write the approaches for people who don't know the area, and don't fudge it - you will be found out
Hope this helps a little,
Chris