I want to get into app developing what are my costs?

Hi i'm a young teenager that wents to get into app developing. I don't want to hire team or anything but rather learn and make my own app.

1. What will be my costs?

Android or apple which should a i make a app for first?

Also my ultimate goal it to make money from my apps so should it be free or priced at $0.99.
Thank you

Added (1). I have a laptop
also a iphone
so please don't include those into the costs

Which sim card to get for iphone?

If i just want to use the iphone for internet (when i have a Wi-Fi connection) WITHOUT a phone plan… Do i need to get the prepaid micro sim card or the postpaid micro sim card? Or does it even matter

IMessage refuses to send, how do I make it send?

Sometimes it sends, other times it doesn't. I have an urgent message I need to send and my cellphone is pay as you go and doesn't have enough time to call or text (text free app calling feature doesn't work on the Internet here, and texting on there won't send right now either).

Don't say something stupid like call 911 to tell them you need to make a call cause you're out of time, they'll think I'm a complete idiot and probably count that as abusing the 911 system.

Also, don't say use somebody else's phone because that's not an option right now.

Added (1). it's on iPod Touch 4th generation, iOS 6.1.6 (my hardware isn't capable of getting iOS 7).

Added (2). Doesn't have SMS, it's not an iPHONE, it's an iPOD TOUCH.