It should be noted that this deal is only available in the US. If you don't yet have an Xbox, but are interested in purchasing one, both of these price points represent a discount over purchasing a console outright and paying for these services individually. It's a financing program, rather than a subscription service, which means that you'll sign up for a two-year contract and then get to keep the console at the end of the period.
Microsoft is billing this as a limited-time offer, and that it's only available to "qualified customers," according to Variety. You can create a deal with any Xbox bundle that suits your fancy; you aren't limited to certain models. Of course, the monthly price will differ if you choose a more expensive bundle. If you cancel before the two years are out, you'll likely owe Microsoft for whatever portion of the hardware you haven't paid for.
Update (11 AM ET): This article was updated to reflect Microsoft's official post.