It all depends...
In the Wii, you're looking at slightly higher than PS2/Xbox dev costs. Of course, that only applies to the typical "video game" type of games. In situations like Trauma Center or other extremely simplistic games (think Brain Age), it's much less. They could probably sell 100k and still come even... Which is part of why there is so much shovelware on the Wii (the other part being that Nintendo does not have a quality certification program to publish games on the system... and people call MS and Sony whores. In Nintendo's world, you pay the fees, you publish the game. Probably a layover and compensation from when they pissed off every third party dev in the world during the 80s and 90s.). :D
In the 360 camp, information like this is a little more available. Capcom has gone on record by stating that they needed 700k to break even on games like Dead Rising and Lost Planet. Considering the top-shelf nature of both these games, that's a pretty good benchmark. Maybe a real blockbuster like Halo or Mass Effect needed more but at least we have a number to work with from Capcom.
In the PS3 camp, things are more ambiguous but don't expect them to differ much from the 360 camp. From most reports, things are a little more expensive to develop on the PS3 but they're close to on par with 360 development. Use 360 numbers and maybe fudge it a bit north and you should be okay.
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