I don't own a kopykake since my cookies making is purely an hobby! But I bought and use the Camera Lucida App which is availabe for iPhone and iPad at € 4.99. As Judy mentioned before, it not projects the image but while looking at the screen of your device you see both the image you want to reproduce and the surface below (i.e. your cookie and your hand).
At first I thought it was more difficult to use, because you have to watch the screen and not your hand. In reality, it's very very easy to use with huge results... and it's very very cheaper than any projector.
Of course you cannot pipe directly on the cookie, you need to trace it with a marker... so this could be a con if you have to do a lot of cookies!
I suggest it to everyone who cannot afford (for different reasons) a projector! 
But you need to buy an iPad or iPhone to use it, right? I've used it and think it works best on the iPad . . . less awkward, as the screen is bigger. For some people, the iPad or iPhone could be a big investment.