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1) Apple's dev license is necessary to upload to the App Store and it costs $99. So it only costs that amount of money to get started making and distributing apps. If you go here https://developer.apple.com/library/ you can learn how to develop apps. It is supper easy. Any who charges you money to write source code is ripping you off. In fact, because you are a businessman with nothing but potential, you should charge them. That's a great way to make money and fund your business. Be sure to mention this on upwork.com
2) I have an app in the Productivity section which has about 3 downloads per week. It is unranked. Using Excel's formula to dermine value from ranking, an app ranked at No. 1 in the app store should make Infinite Money. Since Infinite Money is obviously impossible, then we can discount that result, but remember, Apple fiscal Q1 2016 was $75.9B revenue. So if you have an app in the Productivity section you can make between $0 and $75,000,000,000.
Also, I can tell you forgot about Marketing. Tsk. Tsk. I can help, though. Here are some tricks to kick it up an notch, and really get that edge when sending out your press release and help your software development:
a) Be 12 years old.
b) Be a girl.
c) Be from a place in Syria or Afghanistan where Islamic extremists have declared war on western education.
d) Sustain a near life ending injury in the head. But survive to give talks at the UN and around the world.
e) But a Macbook made after 2009.
Of the above, I think (e) might be the most limiting factor if you primary use a Windows computer. It is just so different.
There are really too few apps in the App Store which accepts "data" and then "generate a visual graph over time". It is a tough problem few developers have been able to solve, and there is a lot of customer demand for inputing "data" on a touch screen device.
Anyway good luck. I'm sure you will be a success.
It's been a while and I thought it would be good to re-visit the "How much do you make from apps" question. Who wants to go first?