Build an excel spreadsheet with dropdown boxes to form a price list for custom build computer cables

I need an excel spreadsheet for use by my customers, It needs to allow them to work through 6 key category choices, each category with less than 10 variables unique to category, however the last category is length in meters, so is infinitely variable I envisage the customer answering 6 questions via drop down boxes, & at the end having the cost of a cable, based on their choices. It needs to be built in such a way that I can adjust the base prices for the calculation easily, however they need to be locked so customers can not adjust. As it is for customers use it needs to be simple to use & look professional