Monthly Billing Portal

I need a portal where my Users can keep records of their customers monthly billing. And i will charge from my users depending upon how many customers records he is saving on my portal e.g. If a user has 5000 customers, I can charge a fix amount per customer from my user. This rule will apply on each of my User. 1. I will create new user. Each customer will get unique billing id too. 2. Each user will enter detail of each customer by 'Add/Edit New customer'. This will also include a field the 'Monthly Bill amount'. This amount will be the amount that customer will pay each month. There will be tax field & total monthly bill etc. fields too. 3. Each monthly Billing will be generated at the start of each month. 4. Delete Customer form. etc. There will be many such forms. 5. Currently, Payment entry is manual form. My User will do manual entry for payment received. 6. List of all customer which will also display customers who paid & who not paid. 7. I need many different reports too e.g. Total monthly earning, Total amount Due, Customers who not paid from last 3 months etc. etc. Above tasks are not all tasks, We will discuss more after selecting a bidder. A.) Coder who has experience in Billing type web-sites will be preferred bcz there are lot of things in Billing sites which an Experienced person can understand well. Please show me examples. I will prefer Joomla bcz joomla has very good backend & many extensions are there to expand my portal. Regards,