Usually I pay £7 for 1000 through the Wii Shop itself. But lately I've been looking on Ebay to see if I can find some cheap cards. I just got 1000 points for £5.
I refuse to pay over £7 for Wii Points otherwise I may as well just get them through the Wii Shop. But even so, £3.50 for a NES game on the Wii is better than £4.50 for a NES game on the 3DS, although I do miss the save state function from the 3DS.