$20 with a Nunchuk
For those of you who somehow don't have a full set of four Wii Remote Plus controllers, Nintendo is selling a refurbished bundle pack of remotes and Nunchuks for $20. As a reminder, said controllers will work on both the Wii and Wii U. You can choose from white, black, and blue.
Keep in mind that pretty much every Wii U game has an alternate control scheme using Wiimotes, so a few wouldn't be a bad investment if you're just rocking a Gamepad.