mobile app developer

I have developed the layout of a mobile app in Adobe XD and I have mapped out the database structure needed for the RewardsRuler app. I have redone the logo and I am now in the need of constructing the databases and building the API’s that connect to the apple wallet. I need to have some basic security in the app, including secure login, behavioral tracking, and full encryption using AES256. The app must be native and secure.
The RewardsRuler app shows the user the best rewards by displaying the card with the highest rewards value on purchase. The user can also manually search for rewards per merchant.
I am also looking to integrate a financial tracking system that shows the user purchases and rewards per purchase and allowing them to set limit alerts in different areas such as groceries, entertainment, etc.
I am looking to connect the banks and credit cards starting with Chase since they have a developed api program. I would also like to add business rewards programs that also trigger at time of purchase.
I know this is a large back end project so we might have to split this into multiple pieces.
Let me know the overall cost and what it would take to get the basic app started. I think we will start with an iOS app and make the android app down the road.
Let me know if you have any other questions or what I can do to help develop more so you can focus on the back end and API’s.