In nintendo's developper website I found this quote.
Q: How much does it cost to develop on Wii U?
It’s free of charge to participate in the program and to submit games to Nintendo for technical certification. There is some cost involved for Wii U development hardware, but we run a program to help developers who are just getting started.
Now is it necessary to get those dev kits? I mean if I have my own personal console. Use Unity libraries (for example there is a ready .dll for using the WiiMote ), am I obliged to get the dev kit? I plan to develop my game using unity if that makes any changes.