ez Form Calculator is an intuitive multi-purpose form creator for WordPress. You can create simple form calculators, advanced cost estimators or extensive contact forms for both yourself and your customers. Easily add basic form elements like checkboxes, dropdown menus, radio buttons etc. with only a few clicks. Each form element can be assigned a value which will be calculated together automatically.

Demo: http://codecanyon.net/item/ez-form-calculator-wordpress-plugin/7595334