Android and IOS versions of Unity are free until April 8th
store.unity3d.com
Usually they are $800 together. (Their site has been crushed...so be patient :)
store.unity3d.com
I'm going to give unity another look in, but the unity servers seem pretty well hammered at this point!
The Apple developer license, Corona/Gamesalad, etc. are far more affordable and less risky. I'm not even sure if you had access to the iOS/Android API without purchasing a license, so I guess you wouldn't be able to practice it.