Truck Transports company billing software or webapp...

I looking for a very simple Billing module intended for presentation to a transport company here in Chennai. The work to be done is as simple as we do in MS excel. I am planning to make it a webpage in PHP rather than a desktop application which could be easily run offline through WAMP. Programmer only needs to enable the user to make entries of daily transactions in a data entry form in various fields, maintain customers, ability to include additional companies, auto-numbering the invoice (and allowing to edit the same), summarize their billing, dig into outstanding invoices/bills, paid invoices/bills, outstanding invoices/bills and will be able to do simple arithmetic & logical functions on data like summation (total), selection on any item to view entire related data, sorting data by date / value, etc..., mail invoice/bills as PDF attachments to their clients & take invoice/bills prints. Please provide a working DFD model, sketches of screens (if possible), etc. By default the application will run offline through WAMP and a PHP script. The application runs offline like a normal web page by simply opening the given local URL and entering user name & password. Please tell me how much time and money u need for this simple one. Programmer must be online at least for 2-3 hours between 10.30 pm - 12.30 am by Indian time and should have chat facility for smooth communication. Your suggestions are most welcome. A very basic sample is "[login to view URL]". Of course, [login to view URL] is huge. Expecting not that much in size.