[fbailey]

easily solved:

Buy this book for 10$ on amazon.com Buy this book for 13$ with your itunes account*

*explanation

[Dylanlacey]

This is the first solution I hit upon: show the user the pricing of each option and see what happens.

I wonder what creative solution Apple will come up with. Bah, it won't be creative, it'll be:

* An app will not charge consumers more to purchase content in-app then they would in other locations.

[memetichazard]

Amazon responds. Buy directly from Amazon.com and receive a 30% credit towards your next Amazon purchase!

[Dylanlacey]

Touche.

[DenisM]

$14.28 :)

And Apple does not allow fractional prices.

[fbailey]

Well you are both more right than me - we can probably settle for 15$ which makes it even more impressive for the user

[xenophanes]

$14.29 on iTunes

Math ftw.