First, I recommend having someone who is either a member of your company or hired in a contract CTO / development management capacity who understands the mobile space so you have a check and balance to ensure you are getting what you paid for.
Second, when creating a mobile app, you have the option to "go native" which means to build the app for Android / IOS using their tools. There is also alternatives like React and Cordova where you can build a mobile app that uses web technology, which can reduce the cost.
If you are still in a heavy discovery mode, I recommend the latter. You can build one app for multiple platforms and make changes much more quickly.
If you would like to know more about my experiences in using these type of tools, please message me.