About $10. Sorry, I couldn't resist!

But seriously...in order to whispersync the last page read, bookmarks, etc. between a personal document on multiple devices/apps, you must place the document in Amazon's cloud by emailing it to your account. Then you can download it to the various devices that support "personal documents" and whispersync.

For more info, sign in to your Kindle account then click the Personal Document Settings link in the left sidebar to go to the Personal Document Settings page. Plenty of info their.