accounting software modification

My client requires me to choose and edit an accounting software for his business requirements. The client is a milk distributor and handles not more than 100 customers (catering and retail), with just one main supplier (local milk produce company), and around 30 products. The client is not very internet friendly, and he normally types in everything on pre set excel sheets. The client owns 2 delivery trucks, so he needs to assign a client to a truck, with the ability to easily change a client from one truck to another. He now wants a system whereby he will; 1 - Enter all products (all products may be sold in single units or in boxes, and have two different price ranges. Each product has a price for caterers and another price for retailers, depending on customer type. Products may or may not be vat applicable, so client will have option to add vat to product or not when listing it. As well, certain products are priced by weight, therefore weight of product must be entered near quantity - example; 1 box cheese - weight 1.297 kg - Price ????) 2 - Enter all customers (all customers, with all their detailed information such as address, contact person, contact number, vat number, and marked as caterers or retailers, and belonging to distribution truck 1 or 2) 3) Daily order sheet - Fill in a daily ''excel like'' sheet, where on one side (rows) the client will have customer list, and on the other side (columns) he will have products. Along the product columns, there will be one column which states which distribution van is the customer assigned to as a standard, which can easily be changed from the same sheet. This sheet will be called daily order sheet. It is important that when a cell is clicked on, the entire row for the client is highlighted to avoid inputting mistakes. 4) refunds - some products come in special boxes which when returned to client, customer will get a refund for. Other refunds may be given for returned products. 5) Produce reports, invoices and so forth. Once saving/ exporting the ''daily order sheet'', all data will automatically be converted to invoices. Other reports which the client may require are; a) daily order to supplier b) list of customers per truck, including one column which states the full price of invoice, and another column which is to be marked as paid or unpaid. c) weekly statements for non cash paying customers 6) Bills - After finishing the milk distribution exercise to all the customers, the client will access an area for billing, where a list of invoices in found. Invoices will have filters such as - today / pending / paid / search by customer/ invoice number. When seeing the invoices list, the customer will easily be able to change the status of an invoice from pending to paid -------------------------------------------------------------------------------------------------------------------------------------- While these are the immediate requirements, more might be required in the future such as pay roll and other requirements. For the time being, the above mentioned requirements are what the client desperately requires. I am not looking for a custom solution, but all i require is help with choosing the right software and its editing. There are hundreds if not 1000's of software already available for a very small price or free on internet which have more functionalities than i currently require.