Hi,
I think a cyborg like voice would be cool for this project. 
Besides the fact that a cyborg is a human augmented with cybernetics and as such will talk just like you and me

you might try to find a software filter that does post processing of the output from the speech routine.
A four quadrant multiplier should enable you to get a very robot-like voice and even a chopper could be used for some really retro-robot-voice results.