Xamarin App in IOS and Android

General information for the business: We are small development agency
Kind of development: New program from scratch
Description of every module: The basic app sections are:
1. Login
2. Depots
a. Listing
b. Detail
c. Map view
3. Work Sheets (version a)
a. Listing
b. Details
c. Sign In
4. Work Sheets (version b)
a. Listing
b. Details
c. Sign In
Description of requirements/functionality: 1. App needs to be available for IOS and Android. We do not want to use Xamarin forms for this particular project.

2. The app must be simple and intuitive. General screen shots/layouts for each section will be supplied.

3. Lizard Design will provide API functionality to bind and receive all data requirements.

4. The app required secure login via the API supplied.

5. The app is required to poll (polling time to be determined) and send back Geo coordinates to the API

6. Some sections are required to be available offline if no internet connection is detected, although functionality will be limited, details of this will be specified, it is proposed that the data that is required for the limited functionality is stored using SQL Lite while there is an internet connection and then this data is used when the internet is not available, when the internet is next available any data stored in the SQL Lite DB will then be synched via the API.
Specific technologies required: Xamarin - IOS - Android
Extra notes: We are a small development team and are currently developing a similar app in Xamarin but do not have the resources to complete this addition driver app.

We are looking to expand our world load without expanding a team and so are looking for long term relationship for this type of project plus a supplier that we can hire to fix/help/advise any issues with other apps that we are currently working on in Xamarin.

I need some costs and timescales. Please feel free to email any questions but at this stage I have kept fairly simple until I receive projects costs.