Nintendo's Online Service will cost $20 a year

Since the Nintendo Switch presentation there have been questions about the online service for the system and how much it’d be and will it be worth it.
Well Nintendo’s price for online gaming surely beats Xbox and PlayStation at $20 a year as opposed to $60 a year. The online service will only be $3.99 a month as well.

Nintendo’s online service also got delayed to 2018 interestingly since it was aimed for Fall 2017 originally.
“You’ll be able to play compatible co-op and competitive games online by signing in with your Nintendo Account. Online play will be free for Nintendo Account holders until our paid online service launches in 2018.”
Nintendo Online multiplayer will remain free until 2018, when it launches as well.

Also at first Nintendo stated when you subscribed to their online service, users would get a free SNES/NES game for a month, but according to today’s update it seems like you’ll be able to keep it.

Source