I've been using a php powered cms system by webassist corp to have clients be able to add and modify content on their websites. It recently went up in price, but it is a bit nicer than the older versions. So if you want to be able to modify your static sites ( any site that is not a wordpress site for example ) I can still recommend it, but it costs a bit more. I generally don't charge that much for installation, since its mostly upload time anyway, but the effort comes into play when the client decides to modify or have the ability to modify all their pages in all regions of each page. To do that requires some effort on my part, so called development time, and that is where the labor fee comes in. Generally I still believe the SEO ( search engine optimization ) for static sites is better than that for wordpress sites, but that may change, as the plugins for WP for SEO purposes are getting smarter, but they also require effort as well. Nothing is simple and straightforward, and does definitely require monitoring, research, comparison and competitive strategies, especially for the more difficult industry niches.
Of course having the CMS is just the first step. The client needs to take advantage of it, and learn to write or change text on a regular basis ( weekly is good, daily is better ) to let google know about its fresh content, as well as the update to the xml sitemap, to let google know about the fresh content as well.