The c1 should work, I've never used it, but there are some videos on YouTube that get pretty tune crazy. $235 might still be a bit pricey for a gag. (At least for me!)
They're now $129 everywhere and if you buy before 12/31 you get a rebate of their free mic. Which is the MP-75 that has a button on it so you can activate the auto tune live on the fly with a push of that button rather than having to step on the pedal. Pretty good deal!