I just recently purchased a Microkorg Synthesizer/vocoder -- low cost compared to most vocoders at only $400.00/new. I've been working with one of the settings and have pretty much perfected the cylon sound. If you've got the change to spare, it's a perfect way to get the sound you're looking for. If you'd like, I can send you a sample.
A dedicated "Cylon Voice" vocoder app is now available for the iPhone, iPad and iPod Touch. This app transforms your voice into that of a deep, metallic Cylon.
Two ways to create your own colon voice and use it in your own project:
1) Sampler: record your colon voice and send it by mail. Import sound sample in your own project
2) Play in Live mode: speak and transform your voice instantly. By connecting your iphone, ipod or ipad (via headphone jack) to your computer you can provide your clips and music with a Cylon voice.