Compare Cars Calculator For Wordpress

I'd like to add a simple calculator to a wordpress blog site.? The calculator would allow visitors to select a gas only vehicle from a drop down (which I could populate) and compare it to a hybrid vehicle (again, I would populate the hybrids and there are only about 20 available today).? Next to each vehicle in the drop downs would be a number, representing the average gas mileage for that vehicle. Once the visitor selects the 2 vehicles, they could then select how many miles they drive each year (again from a drop down of about 5 options).? Lastly, they could select the price of gas from a drop down (probably about 5 options here as well.) The calculator would tell them how much money they would save in a year by choosing the hybrid over the non-hybrid car, or in cases where the non-hybrid car gets better mileage, it would show them how much more it would cost them to drive the hybrid. Once this is working, I'd like to bid phase 2 of this project, to possibly add more funtionality.