I need an budgeting tool in excel

i want a spreadsheet that will allow me to see what happens to a set of sales figures when i alter prices. i want to be abel to add up the margins, cash generation by product by month and overall for 12 months. there are about 20 or 25 products and we sell between 1 and 20 of these a month. i want to be able to play with the % discount and sales mix to see what happens. i want to add to all these products a single "cost" figure as well to give me a net contribution. happy to talk about it if need as i know what i want.