Who else already has a similar app up and running?
List all the apps on the App Store that are similar to yours or even just have a single feature that matches one of yours.
Once you have the list, place them in order from "most like yours" at the top to "least like yours" at the bottom. Write a short analysis for each one stating what it has in common and why yours is better.
Make a note of the price of each app and try to place where your own app should be priced. If it's miles better than the top of the list, you could reasonably charge more for it. If there is a close competitor then you should be similar in price.
We'll call the price of your app the Product Price.
List all the apps on the App Store that are similar to yours or even just have a single feature that matches one of yours.
Decide on your Product Price.