I have linked to a few blogs below who have swatches to help you decide which ones you want to pick up.
Also Farmers who is a major OPI stockist is having a sale on this Thursday (I think every Thursday actually) with 10% off cosmetics. So if you want to get it a little cheaper, Thursday is your day. If that's not cheap enough for you I think they range for about $14-$16 on TradeMe (NZ and AUS only), but the Black Shatter is on there for around $30 or so. Might be cheaper in-store, I don't know yet. :)
I am still on the fence if I actually like them or if it is just the hype, glitter and shatter.