Maintenance after the site is launched
If you have me develop your site on the Content Management System I recommend, Webvanta, you can choose to maintain it in-house or have me do it.
When I use the Webvanta CMS, I offer clients training, a customized step-by-step manual and a certain amount of time baked into the project for future training (such as for those quick, "I can't remember how to do this" questions.
I don't leave my clients with a site they are too terrified to edit or make them search for an answer to a question for an hour that I can respond to quickly.
If your site is not using a Content Management System, I will need to maintain it or you can hire another qualified Web developer. I would not recommend you maintain it yourself.
Even though I do not recommend a static site (meaning one that is never or rarely updated), if this is the case you may not need any maintenance.
If you wish me to do updates and edits for you, the costs depend on how frequently (such as: every month or week) and how much needs to be edited. If you envision regular updates, you could buy bulk hours from me which may be less per hour than as needed.