FYI: DIY RPCube PDQ
There is a lively discussion on how to roll your own (pretty easily and cheaply) happening in the Strobist Flickr group discussion board.
All you need is an SC-17 or a multi-flash sync cord (or generic equivalents of either) and a stereo miniplug. (And just one $10.50 multi-flash cord will make two "cubes".)
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