According to THQ, the cost of developing games for the Wii are much less than for developing games on the PS3 and 360:
Farrell also talked about developing for the Wii as opposed to the Xbox 360 and the PlayStation 3, noting that it was far less expensive making games for Nintendo’s console. Farrell prefaced his [...]
"Wii to Cost Less to Developer for than PS3 or 360" - 07.05.06