Re: Tornado protection: Storm rooms
It just has to be big enough to hold you and your cats, like the lady in the article. Trying to plumb it might be difficult, but I'm no expert. You could also outfit it as a storage closet (don't fill it up!) or better yet, a pantry.
Even the small ones probably cost more than $5,000, but it can be added to the value of your home as an improvement and maybe financed as a home improvement, too. Heck, if you work out of your home as a writer, you might be able to deduct it as a home office expense.