Honestly, it would not work out cheaper in the long run. With dupes, you might not get the color pay off you get with the real thing. You'll end up using more of another shadow to built up the color instead of just using a small amount of the real stuff.
I'd definitely go with the real thing, I've wasted so much money trying to buy knockoff stuff that I've learned the real stuff is so worth it. These colors look beautiful on, blend well, and stay put :)
A great dupe for this is from CoastalScents.com. Its the Revealed Palette which retails for $19.95. It is actually a very close dupe for Naked and Naked2. I have the Revealed palette and both Naked and Naked 2. The Revealed is actually is my go to. I do love the Urban decay palette but I find the other palette to be more convenient.