Develop a iot based offline android app

Hi,
I have a project which is a wifi weighing scale. Using nodemcu + hx711 + 100 kg load cell.

I need an Android app which will work without internet, which can do the following tasks.
1. The load cell data from the nodemcu is transferred through wifi to Mobile phone using serial communication over wifi. This data is of crop harvested by a worker in an agriculture land.
2. The worker who is cultivating, shall have to be authenticated by face point recognition.

The mobile phone will contain, the following stored master data, worker data with face points, workzones, workcodes, category/book.

The Process :
1. Mobile will fetch the load cell data via wifi, authenticate the worker using face point, capture manually the Session wise(4 sessions) data as workzone, workcode, date, time, operator, mobileid from operator input and process each data & store in local database.
2. At end of day, the data has to be frozen/ finalized and can be viewed & downloaded only.
3. Download file options csv, xls, txt. (filename starts with mobileId plus the date.)
4. Download file contains all data captured above, of each worker with all sessions combined in a single row in a day.
5. Also provide option to delete the previous data.
6. Local database should preserve the data for at least 7 days.
7. File can be downloaded by wifi or usb cable to PC OR can be synced to cloud server.

Please give me your quote, with the money & time required. Our budget is minimal. We shall start immediately.

Ask me as many questions before giving your quote.