What you need to create an app:
- You must register as a developer for $99 a year, as already explained
- You must have a recent generation Mac computer capable of running Mac OS X 10.11.x (El Capitan), so you need to factor that into the cost
- You need the XCode integrated development environment, which is free in the Mac app store
- If you are not going to write the application yourself you need to include the cost of designers, programmers and testers