Paid DLC is something that Nintendo has never messed with, but that changes next year with Fire Emblem for the 3DS. According to Nikkei, Nintendo will launch its first ever paid downloadable content some time next March. The report says that this DLC, an expansion, will cost "several hundred yen." Expect future DLC to be at a similar price point.
I like that Nintendo is saying that this and future DLC won't make it any easier for gamers to make their way through games, like the cheat crap in Facebook games. That's dirty territory.
Nikkei also says that the Wii U will see paid DLC when it comes out.