There is an easy way to get some raw numbers. Take the average hourly rate for a dev and multiply it by 8 for every small item on your app feature list you have. Then multiply the result by 2 and you have your app ready for testing. Then the same for the bug fixing and so on.

• design for a webpage layout for one screen (designer)
• the same screen cut into pieces for a HTML (front-end dev)
• some moving parts in this same screen (back-end dev)
• blockchain integration for the same screen (blockchain dev)
• and so on...