Yes, there is a difference between the price of android app and ios app. Generally app development cost is a complex issue and requires very a detailed approach. To know more I recommend to read an article in the link above. There is a comprehensive material about this subject
I give you cost of both apps separately..Hope this will be helpful to you.
On an average, cost of Android app ranges between $15,000 to $40,000 with an hourly rate of $15-$25.
It depends on app complexity, features, frameworks, design and other factors. $3,000 is the very minimum price for a small project. Consider $5,000 to $20,000 cost range for average feature app
Yeah, especially when there are security concerns related to how you manage user authentication and data. If you don't want to rely on 3rd party providers, rolling your own auth system is challenging for developers and gives them more responsibility and that require costs (related to salary).