Hi Susan,
I'm not personally familiar with CharityAdvantage.com, but I did a quick search of the forums and there were a handful of threads where they were mentioned. This one, in particular, may be of interest. http://forums.techsoup.org/cs/forums/p/18336/73375.aspx#73375
I've personally worked with a number of different content management systems, and for a nonexistent budget (which it sounds like may be the case for your needs), I've had really good luck using www.wordpress.org as the CMS and finding a free graphic designer or web developer on a local 501 Tech Club list who helped create a banner to use with one of the pre-existing templates. These "affinity groups" are local listservs of nonprofit tech pros and novices in order to share news, compare notes, job hunt, etc. Even if there's not one in your area, you can subscribe to one of the bigger groups (DC, NY, SF) and see if someone would be willing to volunteer some hours to virtually help you out from another city.
The only real cost to setting up a site is registering and paying for your domain name (that's in order to not have to include a "wordpress" in your URL).
WordPress is open-source, free, pretty easy-to-use, has loads of plugins to enhance your site, but it would require either people internally to set it up or for you to recruit some volunteers.
I'm pretty non-technical myself and created a quick website for my sister's little photo greetings side business using WordPress. It took a couple of hours to get the basic template set up and to upload her "banner" image, but for a no-cost solution, it works for her. She's totally non-technical and she's been updating and maintaining it herself for the past two years, since it was created!
We have a recent article comparing different open-source options, including WordPress, that our friends at Idealware penned. It might give you some useful advice if you choose to look at an open-source CMS option.