Make sure you sit down and talk with the client as to what he wants to be able to update, does he want users to be able to leave comments, a photo gallery, a blog, articles/pages, spam filtering, a calendar, etc.
Based on what he wants, you will need to find a CMS that either fits, or one that can be modified with plugins to make what he wants happen (or one you can modify to add these features).
So that will help you determine, do I use Joomla, WordPress, Perch? Which will help with pricing. For example, I would charge less for a Perch solution, than a WordPress/Joomla solution, because I can tie it into a theme far faster than I could with Joomla and WordPress and I would have less training to provide to the client (Just my Opinion).