<p>I have a site I'm working on that has an event page.  The owner wants to be able to edit the event page weekly.  Would it be easier to teach the site owner how to edit this one page and upload it or use a CMS just for this one page??</p>

<p>Apart from a contact form that posts to an email addy, the rest of the site is static.  Therefore I'd need to add in a db to store the username and password for CMS login.</p>

<p>If CMS then which one would be most suitable for this case?</p>

It depends on the complexity of the page. If it's a fixed structure where the client won't want to add links of photos you may want to give them the ability to edit a simple data file (not the page itself). Then read in the data file. I like to use a simple JSON format for this type of thing.
At least with a data file you can revert to an older version or handle the error gracefully, rather than having the client break the whole page.
If you want to go the CMS route,
Drupal
has a very well-established comunity with plenty of add-ons.
If you're more into roll-your-own programming, you can also look at the
Google Calendar API
,