Build a New Tracking/Control Application with financial tracking

General information for the business: We sell pallets of overstock and customer returned products from many product categories
Database management system (DBMS): Microsoft SQL Server
Description of requirements/functionality: A joint venture is in place between two small companies to purchase pallets of mixed products and sell them on. Invoices are raised between the two partners whenever ownership of pallets is transferred (usually done in bulk). Further balancing monies become due on the sale of a pallet based on the profit of the sale, the expenses incurred by each party and any invoices already raised between the parties (eg ownership related invoices). Further invoices are raised to request settlement of the outstanding sums and the overall balance of credit/debt between the two companies is tracked (currently manually)

A database solution is required to
- track and control the life of a pallet from creation to sale
- track and control the financial balancing (ie invoicing and payments) between the two parties.
- Record all financial data as soon as it arises or is created (eg Expenses, invoice numbers & amounts, etc)
- improving correctness and accuracy through the use of data validation and hiding invalid workflow tasks or data options.
- automate the balancing calculations and assist their inclusion in settlement invoices (through listing uninvoiced amounts)
- track all pallet-related costs through to invoices and payments
- track overall balance between the two partners
- minimize the need for management intervention. (NB. Management attention should be required only for flagged discrepancies, management reports and management-in-confidence setup parameters (eg sales commission rates)
- keep historical records
- provide management reports

The system will NOT be required to
- raise invoice or formal transactional paperwork. Existing accounting systems will be used for this

We have IUR with Microsoft Azure so we would prefer to host the database there. We have very little experience of Azure so we will need strong advice on setting up this service.

The frontend application(s) must be as platform independent as possible as the potential users have a wide variety of environments from Windows XP through to Windows 10 with full 64-bit MS Office suite. Compatibility with mobile devices (tablets) could be useful but is not essential. Please explain your recommendations.

For this project, we would prefer a UK designer/developer so that we can visit each other if needed.
Specific technologies required: Microsoft Azure
Extra notes: A requirements document will be available shortly to convey the user needs more fully. However, some degree of iteration/prototyping should still be anticipated.

Source code should be well commented to assist future understanding and maintenance

Source code should be put under source control from first formal version

I would prefer a fixed cost but I appreciate that this will be difficult if there is any iteration makes this difficult. We are a small company and do not have unlimited budget. So I would appreciate it if you could provide me with the following info:
- your expectation of total time and cost
- how soon you are available to start and how many hours per day (or week) you expect to have available
- your relevant experience of Azure, SQL Server & frontend application development
- Are you an individual or a company?
- If you are a company, how many developers do you have that can do this project relevant employees (in case of non-availability)
- How do you intend to test the application