I am not sure what I would charge for exclusively SEO work because I have never done just SEO. Personally I tend to view most "SEO specialists" as snake oil salesmen, but to avoid going down that route, you should be forward and clear on how you're improving his online presence if he decides to ask about it.
The amount of SEO work will depend on the breadth of the website's content, and how often it will be updated. If his website is going to be constantly updated with new articles, you will probably need to pump SEO regularly for his site to fit in with the new content. However, if the site only exists to sell his services, you can just focus on that part.
Also, the ease of automation depends on whether his site is completely custom-made from the ground up, or if it is built with one of the more popular CMS packages. Joomla and Wordpress, for instance, already have several modules or plugins that make SEO work more accessible to people that don't know how to do much more than use a WYSIWYG or fill out online forms.