How to make the invoices under certain amount? If exceed there should be a warning.

I needed to cater below requirement using inventory, order management, fixed asset and General management.

For example:

• A company pay $ 10,000 to a company and that company payback $ 4,000 after 6 month.
• During that period the company have do few expenses such hotel bills, food expenses, air tickets etc.
• Company have to manage above expenses under that receiving amount ($ 4,000).
• The difference between receiving amount and sum of expenses is consider as project profit.
• The company requirement is they have to track those expenses related to project and not to exceed the receiving amount.
• In addition, company needs to make invoices to each expense.