You could pay around $150 for app development.
Or $20,000.
Or much more.
It depends on what all you want to accomplish, and it depends on who you hire.
If you are inexperienced in this area, you will benefit by talking to some different people and getting some additional insight.
I strongly recommend that you post this description of your goals for your app as a job posting on the main Upwork website.
State: "Right now I am only hiring freelancers to consult with. If you are able to provide me with realistic, helpful insight about how best to develop this project, then please apply. You may apply to this job if you are interested in actually working on it as a developer OR as a project manager OR if you only want to provide your insight as a consultant."
Hire at least 5 different people, using hourly contracts, just to talk to them about your project. You might spend 30 minutes to an hour talking to each one. This investment upfront will save you a lot of time and money in the long run.
When you DO hire freelancers to work on the project, whatever you do... DON'T HIRE ONLY ONE PERSON. That would be a huge mistake. If you only hire one person, you won't have any way to compare his work to the work done by other freelancers.
Your goal should be to work with only the best freelancers on your team, and stop working with those who cost too much or whose work doesn't measure up.
If this is a serious project that you actually want to see finished, then you should hire a project manager.
20% of lead developers are capable of serving as their own project manager. But what if your lead developer isn't among the 20%? Then your project will never be completed. Even if you hire a lead developer who IS among the 20%, it is STILL better to have that developer (and the rest of the team0 work with an independent project manager.
