How many pages on the site and will you need the ability to add more and create links to them or is this just a way of allowing users to alter text on existing pages ?
There are ways of setting up web forms to write to a document on the web server, so a user can open a form that allows them to alter the text as it appears in a textbox. It's a bit limited but works well for reliable and redluar alterations to page text copy. Imagine your page divided into a text area for each paragraph and the user opens that page, alters the text in the textboxes then the submit or save button updates the page on the web server.
Programs like the excellent CoffeeCup HTML Editor cost very little [half price sale at the moment - see the thread titled "Coffee CUP Software DEAL" or click here] and it has a QuickPost feature. This means that as long as you put the quickpost tags into the page when you create them, you can select the page to open using QuickPost and it loads a copy of it from the web server, you edit it in CoffeeCup HTML Editor then when you save it it uploads direct to the web server and overwrites the existign file.
It may look impressive and I suppose that in the face of it, it is. Keep in mind though, that for anyone to use it effectively you'll have to spend time and effort in teaching them how to use it as well as correctly configure it into the web pages/site. It's a pain and, in my opinion, is not worth the hassle by a long shot.
You do understand that to use such a system you need several other things running nicely ?
You need effective authentication set up to disallow access to anyone who does not have permission to use the system.
Your directories will have to be ordered and secured in certain ways for something like htmlArea to work properly.
Your content will have to editable in one or another way, which could mean anything from storing it in and calling it from a database to referencing data text files and allowing them to be written to for updating and read from to include their content in a page.
Without wanting to rain on your parade, there's a lot more to this than bolting on a WYSIWYG editor and letting your site owner/managers get on with it.