Mobile App Developer / Development, iOS, Android, GPS, Real Estate Map Development

I am looking to create a map app for buildings and houses. The purpose of this app is for end users (house or apartment buyers or tenants) to put on the map when they are in an area they like and see if there are any vacant apartments in a building they click on in the app. Once a user clicks on the building, the building name will appear with details on how many vacant apartments there are in the given building. Explained simply. And I want info to be there only if one clicks because or else there would be too much information at once. ( To be discussed and reviewed) Like a Pokemon Go, Or a Star Map, or Google Map combined but for finding out the building names and finding out if there are any vacant apartments in the given building. Eventually what I would like is a type of a star map but instead of looking at the stars you point at buildings and get more info on the building and what is available in that building. Let me know what you understood of this task and how much time would be required for you to complete such a task and for how much. Thank you Is 300$ enough? Do you need more or less?