I'm sure there's a way to do it easily, but nothing comes to mind. What OS? You should be able to 'print' to PDF from the browser.
OSX it's a standard print option, and on Windows I always end up falling back on CutePDF Writer. On linux, cups-pdf does the job (probably already on your system or in the package manager at leaast).
Tedious in that you'd need to do this for each page, but there's definitely ways to process the HTML in some form of automated fashion - I've seen the results though the means are not something I am terribly familiar with.
Hey buddy, I had a Cengage book last semester. I broke the DRM very easily-- get CUPS-PDF and simply print the book from the DRM reader, as it allows you to print anything.