My understanding is that hardware teardowns typically compare to similar parts with known prices and cost is estimated. The best I was able to find on the Wii remote was, I think, last year. This website mentioned that the parts were something like $9 in 2009 or 2010. I don't think that was official or reliable by any means, but the estimate didn't seem terrible off base. I'm too lazy to dig up that old post.
I have no opinion on the whole ripoff thing. I bought an additional Dual Shock 3 controller and will undoubtedly buy 2 Pro controllers if only for the next Smash Bros. game. I'd rather not pay $50 for anything, but that's just unabashed consumerism. The only point I'm trying to make is that after 5-6 years, the price of components inevitably drops. That's just the nature of technology and the passage of time which I'm sure we're all well aware of. Something that cost $50 half a decade ago probably shouldn't cost that much today. It's important to note the difference between what something is worth and what something costs. I don't think any of these controllers (GamePad not withstanding) are using parts that aren't dirt cheap now. Still, every day we pay for things in which the individual parts are worth less than the whole.