There's no real answer to this question without detailed specs. Even then you would only get a rough estimate. But Let's say you got a very inexpensive develop

There's no real answer to this question without detailed specs. Even then you would only get a rough estimate. But Let's say you got a very inexpensive developer say $50/hr for 3 months at 40 hours/week that's 480 hr so it's $24,000 for the 3 months. 3 months would get you a very simple app which would serve as an MVP. At best you can use it to get investors to continue with the development. Putting together an app is expensive and setting up the business to go with it is even more expensive. Good luck!