I would price it at $19, where it would be towards the top-end of indie games on Steam; by the standards of people who enjoy Dwarf Fortress, Dwarf Fortress ROFLstomps the depth and quality of any other $19 entertainment option.
I would then immediately solicit inclusion in a Humble Bundle, in the expectation that Humble Bundle would leap at the chance. One could envision a rougelike or Df-alike bundle; I anticipate that Humble Bundle would give DF top billing in whatever deal was negotiated. I would model that Humble Bundle as doing > $800k in sales, of which DF's take would be > ~$80k. Throw in "and we'll use Humble as our exclusive e-commerce provider for 12 months" since I think it is fairly clear that the authors don't want to be in the e-commerce business; that gives Humble ~10% of their gross revenue for next year.
Stage 3 of the master plan: get the game onto Steam. This might require $X,000 worth of production-ready art and video assets to satisfy Steam's requirements; $X,000 will not be a material amount of money to Dwarf Fortress, LLC.
The above unsolicited opinions are coming from a place of love for small software businesses generally and Dwarf Fortress in particular. Strike the earth.