Converting a Static HTML to WordPress

I’ve been playing around with WordPress for a little while. Nothing big, just adding pages and posts, messing with the css and such.
Well I have a site that I’ve maintained several years now and it is almost 200 pages in size — all straight-up HTML (except an image gallery that I added on a couple of years ago).
I come to the conclusion that it’s past time to switch over to WordPress with it, but I have no idea where to begin.
The URL is http://www.nosaintshistory.com if you’d like to see it.
It’s made up of, oh, about half-a-dozen “sections”, each with a somewhat unique style. So to me, that means half-a-dozen different CSS styles. And as much as I want to switch to WordPress, I’d like to keep as much of the original style as possible, particularly for a couple of the sections.
So, my question is, after looking at my site, how difficult would it be to incorporate it all into a single wordpress installation?