If you at all go for a website, please don't go with a free host blog.
It gives off the impression of being unprofessional, and is associated with unpublished wannabe writers, which is just not your case. Anyone can have a free blog, but you sir, have a published book. If the marketing and success of it matters to you, there should be plenty of options for you with minimal cost and a domain wholly yours--that makes all the difference in how your web presence is perceived. As I said, either do it that way, or just don't have any web presence at all, it's better than a free blog. There is such a thing as bad marketing when your product is quality work--your marketing has to be up to it.
Fatcow, for instance, usually offers some plans for just U$4/mo. or something, but I'd actually do some google searches for "wordpress hosting" and drill down the result pages, there are many companies willing to set it all up for you and charge you a modest price for the hosting. They will usually handle the domain registration as well. I'm not talking about "premium hosting", though I'm unsure what you use it for--you mean a dedicated server? You don't need that. If, on the other hand, by premium hosting you merely mean paid hosting, then yes, you do need it.
As someone else said, make it an author blog and not just the book's blog (but definitely give the book a home inside it), and then it might be much easier to justify the cost.
Disclaimer: this is an answer from someone with more experience in marketing than in writing books.