That sounds like a pretty cool project, are you absolutely sure that a switch like this will work fine with your 360/PS3/Wii?
If you're sure, we'll do it for just the cost of parts: $25 for the electronics, plus the cost of the USB switch, and shipping from the UK to wherever you are (typically $12 international). I'm not sure how neat we can make it, depends on how much room is inside.
However, we would like to fully document the project and release any designs and source code for the project as open source (3-clause BSD) so that others can follow and recreate it.
We are a company that designs and sell microcontroller products for hobbyists, in particular 32-bit ARM microcontroller development boards, and quadcopters. Website: http://www.universalair.co.uk/