The app store version is $25, but the desktop version is free. There's also a free web app that can be used from handheld devices with internet access and a free Android app. You can sync across multiple devices via the web app.
I do most of my Anki revision through my iPhone: I can use it anytime I have 30 seconds to spare. Such as waiting for the dentist, waiting at a pedestrian crossing, waiting for breakfast to cook, waiting in line for lunch... etc.
I'm a very patient person as I'm extremely happy to wait for things now :)