MAC White frost is probably one of most raved about MAC eye shadows. There is the reason for that, it's simply amazing!
Want corners of your eyes illuminated but not overwhelmingly shinny? Cupid's bow enhanced but not looking like you have cappuccino foam above your lip? Subtle glow under your brows? 
White frost got you covered, plus you can apply it before any matte eyeshadow to make it satin. 
You can also highlight your nose with it. You got the picture, it's a great eyeshadow.
 So what about the dupe? Let's get back in time, not to far, just to the time when my makeup collection wasn't so disturbingly big and it wasn't weird for other people to buy me makeup. 
Back then my mum got me Bourjois Little round pot eyeshadow in 90 Blanc Diaphane. Now there is a point to this little flashback. That Bourjois eyeshadow turned out to be the best dupe for White Frost I've ever found. 
These two shadows are almost twins, MAC shadow is creamier so you have to press a brush a bit harder to pick up Bourjois shadow, but besides that they are practically the same shadow! In those countries where MAC is more expensive it definitely pays off to get the Bourjois shadow.