How to Migrate static html files to Book - Migrate Module
A full description of this process would fill a lecture series.  However, the broad approach I would take follows. This approach also has some assumptions that need to be met.


You will need to be able to code
You will need to know, or learn (it's not hard) XPath
The files are in a structure that allows you to recognise where they live in a book (either by links from file to file or path/filename or a combination.


If these conditions are met then import_html is where I'd start.  This will require you have the ability to write a module (that will use this module) and there is a bit of a learning curve, but learning this is well worth it.  If you're already able to import the files it sounds like you're up to speed with the skillset needed.

One of the things that import_html will also allow you to do is update nodes if they're already present too.  Although my experience with this has always been with blowing away the content and rerunning the import to see how any changes went.

I've been involved with a few projects that used this and imported many content types and media from static source dumps.