Simple PHP Application

I have a requirement for a small system. I have detailed it properly because this is a low budget project so please quote according. Basically in the beginning we add around 25 products to the products table. We then keep adding customers whenever we get a new customer. We then raise an invoice on that customer. Each invoice has many products and one customer. We sometimes raise a sales order which is similar to a invoice (has many products, one customer) We sometimes convert a sales order into a invoice. We also record payments for an invoice (an invoice can have many payments). All this can be viewed by simple reports (SQL queries) We will use a Javascript library to do pagination / sorting / searching. Following are the details: 1. login /manage users /logout/ two user roles - sales & admin 2. add customer / edit customer/ view customers / export to csv 3. add products / edit products / view products/ export to csv 4. add invoice / edit invoice / view invoices / print invoice / print invoice + shipping label/ export to csv 5. add sales order / edit sales order / view sales order / print sales order / print sales order + invoice / convert sales order into an invoice (change quantities)/ export to csv 6. add payments / edit payments / view payments (payment is associated with a invoice….payment id, payment date, amount, description) 7. reports -tax report / sales by customer / sales by item / sales by period / invoices by status (paid/unpaid) User - username, password, email, role Product - productID, Name, Description, UnitPrice, TaxSlab, QuantityInStock Customer - custID, Name, Email, Phone, Address, City, Pincode, TIN Invoice - invoiceID, Date, custID,Description, Discount, Shipping, LineItems (products) SalesOrder - Same as invoice Payments - paymentId, invoice, date, amount, description TaxSlabs - taxID, description, amount LineItems- lineID, invoiceID, productID, Quantity, Discount, Total The app should be bug free. I will do the css myself. I will provide access to my shared hosting space, cpanel and FTP. If everything goes well, we will extend the system and this work will continue with more features being added regularly.