Custom Calculator On Wordpress Site

We need a simple commission calculator for a real estate website. The consumer would type in the value of a home, and the tools would calculate the cash back based on the following equation. Home price x 0.25% - $7000 = X The consumer would type in the Homeprice only. By clicking the calculate button, the site visitor would find the product of the calculation followed by a statement such as "Amount saved when using ....". Followed by one line of small print. We would need the ability to edit the CSS to match our theme as well has having all the text editable. This calculator would be positioned as widget on a wordpress site. The widget would have to work with the site's existing theme and plugins.