Build a simple excel program for Windows

Build a calculator program for ms window. I will provide the calculation formula in an excel sheet. The calculation is based on size * cost. The cost is based on a few different selections and also quantity. I attached the screenshot of the program that I want to accomplish. I also want to be able to change (update) the cost in the program from time to time to keep up with the rising cost. So the program must be easy enough to update the cost in it. I can send you the old program that I have now. You can use the old program as a reference or you can modify it. I like to get it done fairly quickly.