We don't yet know what controllers will cost but this being Nintendo, I can't imagine they will be more than $70. If the part cost rumour is anywhere near accurate, it could even be $60, which is the same as the Wiimote and Nunchuk. Parts costs also go down as time goes on, and although we didn't see the Wii's controllers drop in price, we probably would see the tablet controller drop in price if it's more than $40.
It's pretty much a given that whatever Microsoft and Sony's next system are going to be, they will have more powerful hardware than the Wii U. The tablet controller will be its main reason for existing just as the Wiimote and Nunchuk were with the Wii, so you can bet I want support for 4 of them. I know that's not going to happen though, which will make multiplayer games pretty much a Wii with better graphics. That may be fine for most people but I want more than that.
But it's all speculation for now and it's anyone's guess what will end up happening. Whatever it is, it should be interesting to see.
As far as Nintendo's peripherals are concerned, I don't believe they were ever made for more than one game in mind. For example, the Balance Board, I don't think Nintendo ever intended to use this with any game other than Wii Fit, which is why the board is bundled with Wii Fit and you can't buy it separately. Same with the wheel, it was just for Mario Kart, though it was sold separately but that's because Mario Kart is a multiplayer game. Nintendo didn't pledge more support for these accessories so they were not misrepresented, and I have no problem with them existing solely for the one game for which they were created.
The only complicated accessory is the Wii Motion Plus. Not only was the accessory quickly bundled with all Wiimotes and Wii systems, but it was soon built into the Wiimote itself at no extra cost. It seems like Nintendo pushed hard to make this the new standard, but haven't released all that many games for it (though still more than their intended one-off accessories). However, since the Wii U will use Wiimotes, I don't think we've seen the last of the Motion Plus. Who knows, maybe part of the reason they made it the new standard is because they knew it would be a primary controller on the Wii U and wanted people to have them.