Google allows Project Fi subscribers to finance the Nexus 5X or Nexus 6P over 24 months
In addition, Project Fi customers have the option to finance the purchase of a Nexus 5X or Nexus 6P over 24 months. That would make the cheapest Nexus 5X $15.79 a month, while the most expensive Nexus 6P would run $27.04 a month. Google does do a credit check, and will allow you to pay off your phone earlier if you so desire.
All color and storage options for the new Nexus models will be available from Project Fi. If you already are a subscriber, go to the website, click on "Your plan" and go to "Upgrade device." If you have an invitation to join Project Fi, this might be a propitious time, what with the new Nexus handsets and all, to take advantage of the invite.
Meanwhile, some current Project Fi subscribers have been complaining about the lack of handset choices for the wireless operator. That number has just tripled (albeit to three).