The original Wii was $249 and sold tremendously. Wii U launched at $349 and was a complete and utter failure from a sales perspective. Nintendo is trying to re-capture the success of the original Wii and I am certain they will match the $249 price point or come in lower with NX. Paying more than $249 for a portable gaming system in 2017 that doesn't do much of anything else but video games simply won't fly with consumers.
The only scenario I can see Nintendo having where NX costs more than $249 is if they have a "hybrid bundle system" that includes a dock and controller to make it a traditional console as well. If they did this, I still think they would offer the standalone handheld at $249 or below and this would be the main seller. The more expensive "hybrid bundle" would be targeted more to the core gamers and Nintendo die-hards and wouldn't sell as much as the standalone but would have a better margin.
So essentially its $249 or bust.......I just can't see it being successful at more than that...