Android Invoicing App

I require a small android smartphone invoicing app to act as a front-end to an online accounting system

The application will consist of 5 or 6 screens (mostly designed) plus 4 database tables.

The screens are:-

- Initial Menu Screen
- Cutomer Details
- Product Details
- Invoice List
- New Invoice (which consists of 4 tabs - customer details, multiple product details, payment details, summary)
- Preferences

The database tables are:-

- Customers
- Products
- Invoices (which consists of 2 tables - invoice header details, and item details)
- plus, possible, preferences

Completed invoices are to be saved in the database and posted to a specified web address using mark up similar to xml.

The functionality is to create, save and delete invoices, customers and products with an option to save customer and product details each time they are added to a new invoice.

On completion of the project I require the source code so that I can make any subsequent modifications.

At this stage I would like an hourly rate and an indication of how long the project might take to develop.