In the past few months, we have covered plenty of smart form builders here that you can use to build complex cost estimation forms for your website. The Calculator Forms plugin is also worth a look. It lets you build all kinds of cost estimation forms. You can customize everything with drag & drop.
Calculator Forms can handle math calculations. It support conditional logic rules. This plugin is Ajax powered, so it doesn’t require a page refresh for submission. Users can upload one or multiple files. Customers can even sign for their order on your form. With Google Analytics support, this plugin can track all the steps visited on each form.
Calculator Forms supports mod, sigma, log, power, and sin/cos and many other functions. It has a responsive design. rednumber is the developer behind this script.