Yes, a CMS might work for you. Try iUpdateIt to do what you want. This will give you the functions you want and still be able to control what the client can and can't get to on the site. Oh, and if they want a calendar function that works this way, I like Localendar. I like to use more simplified and selective things than a full blown CMS so both of these ideas might do the trick for you without locking you into a big system.