The demand for iOS devs right now is intense. A senior-level iOS dev can command ~$200K or more in the NYC area right now, I imagine the Bay Area to be similar.
Writing an app and selling it on the app store for ${LUDICROUS_SUM} has been a myth for a long time now, but you can still make your $4500 back very, very easily.
But the reality is that even junior developers are making very good money working contract or full-time.
$4500 is less than a semester of required classes at University. And it was a good way to dive in.
Also, a senior iOS developer can make anywhere from $90-150k in even a low paying market like Utah. I don't even know what the market is in places like New York and California.
Needless to say, what you get for your $4500 is a lot more than just indie game revenue. It's a life changing experience to learn to write iOS apps.