Excel template with formulas

We are a cabinet company, we need an invoice that will have 6 columns the 1st will state the item,2ndd contract price,3rd previously billed, 4th current billing, 5th %,6th balance. I need to go in and change the info, numbers, item, amounts, %, etc. Some customers might have 10 items and some may have 50. It needs to go by what % I am billing that month. I have an example invoice that we are manualing doing. I would like it ASAP and we don't have a budget. Thank you