The cost of iOS app development depends on app complexity (take into account all the features and how much time and resources it would take to build them). How complex would its design be? If you’re thinking of custom UI/UX design, that’ll cost extra. Where will you hire the developers/designers from? That will also affect rates. Then there’s testing and debugging, which is also necessary and will cost more depending on the extent of testing involved.
Once you launch, you will have to consider maintenance, updates, marketing, etc. All in all, expect a minimum of $25,000. Different niches mean different ranges, so consult with an experienced iOS app development company for the best results.