Create cost calculating Wordpress Plugin

Hi, all I need a Cost Calculating Wordpress Plugin for my Website, basically I need to ask the Customer for some Values and then calculate using the entered Values and Values from Database, store the calculated Values in the Database and give the registered Customer the option to save result. I saw this Calculator and I like it: [login to view URL] My Website is: [login to view URL] The Plugin must be easy to read and easy to add or remove any fields, basically the most important thing for me is the Layout, I have some coding skills and it will not be a Issue for me to adjust the plugin later. As for now I only give one option to calculate later I will add more.