Most reviewers are clearly affected by the price. They're right, the price for these adaptors seems exorbitant.
The catch is that Apple's patented MagSafe prevents you from buying a universal adapter from a reputable brand.
You can buy a knockoff (I have) from China (i.e., dealextreme), but you have to be very trusting. I stopped using my knockoffs after they started getting really hot. I only use them in a pinch for short periods of time now.