In reply to David Coley:
I think first you have to make a few decisions about how you want your site to be. Is it going to be a static site (as it looks to be now) or dynamic, like a Wordpress site where users can interact with the site leave comments etc. A dynamic site has obvious advantages but requires regular maintenance, updating, moderation etc.
If you keep it as a static site then you could potentially keep the site as it is and make a few modifications to control the look of the site. A key thing would be to add a stylesheet. This would involve one short line of text added to the header section of each page that links to a small text file. With a good text editor this could be done to all the pages with just one command. Then from that one text file you can control the look of the entire site from layout, colours and fonts etc. Theoretically that could be a really quick and easy way to change the site. However with all those pages I suspect there'd be a lot of other changes you'd probably have to make to individual pages and with hundreds of pages it could end being days or weeks of work.
Having said that though I'm not sure what other options there would be that would be easier. The wix site looks like its designed for making the site from ground up so that would take even longer. You'd have to create each page again. And I'm not sure what sort of software they'd be using.
A big question you need to ask is how easy is it to migrate my site in the future? They may go bust or start charging over the top prices. If they're using some custom made propriety software it might be very difficult, even impossible. If they're using something standard like Wordpress, it will be easier. A static site however will be easiest of all. You just ftp the whole site to its new home. Static hosting usually tends to be cheaper or free, though you can find free hosting for database driven sites (eg. Wordpress). eg. freehostia.com
THe other option is not database driven dynamic sites. These don't require a database but do require a PHP server. These have some of the advantages of both. You can edit pages on the fly through a web browser but if you want to move the site you just download the entire site to your hard drive and re upload it somewhere else. Like Wordpress the look of the site would be controlled through templates. Dokuwiki is a popular example.
Quite a lot to consider. Overall though I think I'd avoid anything like Wix.com. Stick to standardized stuff that can be used anywhere and is well supported.