May be a bit late in the game, but I've submitted price matches to Amazon for Gobliiins Trilogy and Ninja Village. I'd rather spend coins.
Also, has anyone tried the free Sherlock app? You get the first 2 cases for free. Amazon has an exclusive promo that gives you access to 6 cases for free until Aug. 19th.
Saw these prices for the IAPs on the iTunes store (wife has an iPhone, was checking to see if she could get the base app for free as well).
Cases 3-10 $2.99
Cases 3-6 $1.99
Cases 7-10 $1.99
If the app is as good as everyone says, I'll just spend the 299 coins to unlock all the cases.